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COMPLETE LEARNING NOTE: ANTI-CANCER DRUGS (PHARMACOLOGY)

From Zero to MBBS Examination Mastery

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SECTION 1: BIG PICTURE OVERVIEW

What Problem Does This Drug Class Solve?

1. Kill cancer cells
2. Stop them from multiplying
3. Prevent them from spreading
4. Shrink tumors enough for surgery or radiation to work
5. Control the disease long enough to give the patient a better and longer life

Cancer cells are YOUR OWN cells that have gone wrong. Unlike bacteria (which are completely different organisms from you), cancer cells are human cells. This means most things that kill cancer cells also harm your normal cells.

"How do we kill the cancer cells more than we kill the patient?"

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SECTION 2: BUILD THE FOUNDATION

Part A - Normal Cell Biology (What Is Normally Happening?)

CELL CYCLE - The 5 Phases

G0 (Gap 0 / Resting Phase)
  ↓
  Cell is not dividing. It is just doing its regular job.
  
G1 (Gap 1 Phase)
  ↓
  Cell prepares to divide. It grows bigger.
  It makes proteins and RNA.
  Duration: ~12 hours
  
S (Synthesis Phase)
  ↓
  Cell copies its DNA.
  Every chromosome is duplicated.
  Duration: ~6-8 hours
  
G2 (Gap 2 Phase)
  ↓
  Cell checks if DNA was copied correctly.
  Prepares machinery for division.
  Duration: ~4-6 hours
  
M (Mitosis Phase)
  ↓
  The cell actually divides into two daughter cells.
  Uses spindle fibers made of tubulin protein.
  Duration: ~1 hour
  
Then each daughter cell either:
→ Goes back to G1 (continues cycling)
→ OR enters G0 (goes to rest/become specialized)

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Part B - What Goes Wrong in Cancer?

• Normally, these genes control cell growth and division.
• Analogy: Oncogenes are like the gas pedal in your car. In cancer, the gas pedal gets stuck down permanently. The cell keeps multiplying even when it should stop.
• When oncogenes mutate and become permanently "switched on," they are called activated oncogenes.
• Examples: Ras, Myc, HER2, BCR-ABL

• These genes put the brakes on cell division and repair DNA damage.
• Analogy: Tumor suppressors are the brakes in your car. In cancer, the brakes get cut. Nothing stops the car.
• Most important: p53 (mutated in ~50% of all human cancers), Rb gene, BRCA1, BRCA2

• These fix mutations in DNA.
• When they fail, errors accumulate faster and cancer develops more rapidly.

• Normal cells can commit suicide when they are damaged.
• Cancer cells lose this ability. BCL-2 family of genes are pro-survival genes that directly inhibit apoptosis. In cancer, BCL-2 is overexpressed, meaning the cell refuses to die.

Normal Cell:                    Cancer Cell:
- Responds to "stop" signals    - Ignores "stop" signals
- Self-destructs if damaged     - Cannot self-destruct
- Stays in its tissue           - Invades other tissues
- Limited blood supply          - Grows new blood vessels (angiogenesis)
- Finite number of divisions    - Divides infinitely

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Part C - Why Do Some Cells Become Cancer?

1. Ionizing radiation - X-rays, gamma rays, UV light (skin cancer)
2. Chemical carcinogens - tobacco smoke, aflatoxins (liver cancer), benzene (leukemia), asbestos (mesothelioma)
3. Viruses:
   • HBV/HCV → Hepatocellular carcinoma
   • HPV → Cervical cancer, oropharyngeal cancer
   • EBV → Burkitt lymphoma, Hodgkin lymphoma
   • HIV → Kaposi sarcoma, lymphomas
4. Genetic mutations (inherited) - BRCA1/2 (breast/ovarian), APC (colon cancer)
5. Chronic inflammation - repeated injury and repair creates fertile ground for mutations

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Part D - Cancer Growth Kinetics (How Fast Does Cancer Grow?)

• 1 gram of tumor = approximately 10⁹ (1 billion) cells
• A tumor must reach ~1 cm (around 10⁹ cells) before it is detectable by most imaging
• A patient dies when tumor burden reaches approximately 10¹² cells

• Each cycle of chemotherapy kills a constant fraction of cancer cells, not a constant number.
• If a drug has a 3-log kill rate, it kills 99.9% of cells in each cycle.
• Start: 10¹⁰ cells → After 1 cycle: 10⁷ cells → After 2 cycles: 10⁴ cells → After 3 cycles: 10¹ cells → Cured

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Part E - Where Can Drugs Intervene?

CANCER CELL VULNERABILITIES - Sites of Drug Action:

DNA SYNTHESIS
  ↓
  → Block DNA synthesis (antimetabolites)
  → Damage DNA directly (alkylating agents, platinum drugs)
  → Prevent DNA repair (topoisomerase inhibitors)
  
CELL DIVISION MACHINERY
  ↓
  → Block spindle formation (vinca alkaloids, taxanes)
  
SIGNALING PATHWAYS
  ↓
  → Block growth factor receptors (targeted therapies - TKIs, monoclonal antibodies)
  → Block downstream signaling (mTOR inhibitors, MEK inhibitors)
  
HORMONES (for hormone-dependent cancers)
  ↓
  → Block hormone production (aromatase inhibitors)
  → Block hormone receptors (tamoxifen, flutamide)
  
IMMUNE EVASION
  ↓
  → Unleash immune system against cancer (checkpoint inhibitors)
  
APOPTOSIS PATHWAYS
  ↓
  → Force cancer cells to self-destruct (BCL-2 inhibitors)

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Part F - Important Terminology You Must Know

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SECTION 3: DRUG CLASS FRAMEWORK

Overview - Classification of Anti-Cancer Drugs

ANTI-CANCER DRUGS
│
├── 1. CYTOTOXIC DRUGS (directly kill cancer cells)
│   │
│   ├── A. Alkylating Agents
│   │   ├── Nitrogen mustards (cyclophosphamide, chlorambucil)
│   │   ├── Nitrosoureas (carmustine, lomustine)
│   │   ├── Alkyl sulfonates (busulfan)
│   │   └── Platinum analogs (cisplatin, carboplatin, oxaliplatin)
│   │
│   ├── B. Antimetabolites
│   │   ├── Antifolates (methotrexate)
│   │   ├── Pyrimidine analogs (5-fluorouracil, cytarabine, gemcitabine)
│   │   └── Purine analogs (6-mercaptopurine, cladribine)
│   │
│   ├── C. Natural Products
│   │   ├── Vinca alkaloids (vincristine, vinblastine)
│   │   ├── Taxanes (paclitaxel, docetaxel)
│   │   ├── Topoisomerase inhibitors (etoposide, irinotecan, topotecan)
│   │   └── Antibiotics (doxorubicin, bleomycin, dactinomycin)
│   │
│   └── D. Miscellaneous (hydroxyurea, L-asparaginase)
│
├── 2. HORMONAL AGENTS
│   ├── Glucocorticoids (prednisolone, dexamethasone)
│   ├── Antiestrogens (tamoxifen, fulvestrant)
│   ├── Aromatase inhibitors (anastrozole, letrozole)
│   ├── Antiandrogens (flutamide, bicalutamide)
│   └── GnRH analogs (leuprolide, goserelin)
│
└── 3. TARGETED / BIOLOGICAL THERAPIES
    ├── Tyrosine Kinase Inhibitors (imatinib, gefitinib, erlotinib)
    ├── Monoclonal Antibodies (trastuzumab, rituximab, bevacizumab)
    ├── Immune Checkpoint Inhibitors (pembrolizumab, nivolumab, atezolizumab)
    └── Miscellaneous targeted (BCL-2 inhibitors, PARP inhibitors)

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CLASS A - ALKYLATING AGENTS

What Are They?

Mechanism of Action (Step-by-Step)

Step 1: Drug enters the cancer cell
    ↓
Step 2: Drug undergoes activation (some drugs like cyclophosphamide 
        need activation by liver enzymes first - called "prodrugs")
    ↓
Step 3: Drug attaches an alkyl group (-CH₂-CH₂-) to the 
        N7 position of guanine in DNA
    ↓
Step 4: This creates a "cross-link" between two DNA strands
        (imagine stapling two pages of the instruction book together 
        so they can never be read or copied)
    ↓
Step 5: DNA cannot replicate or be transcribed
    ↓
Step 6: Cell cycle is arrested, then apoptosis is triggered
    ↓
Step 7: Cancer cell dies

The Bifunctional Concept

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Subclass 1: Nitrogen Mustards

CYCLOPHOSPHAMIDE METABOLISM:
Cyclophosphamide (inactive)
    ↓ Liver CYP2B6 enzyme
4-hydroxycyclophosphamide
    ↓ Spontaneous
Aldophosphamide
    ↓ Splits into two products:
    
    ├── Phosphoramide mustard → ACTIVE (DNA cross-linking, anti-tumor)
    └── Acrolein → TOXIC (causes hemorrhagic cystitis)

• Adequate hydration (increases urine flow, dilutes acrolein)
• MESNA (sodium 2-mercaptoethane sulfonate) - given alongside high-dose cyclophosphamide. Mesna reacts with acrolein in the urine and neutralizes it before it can damage the bladder.

• Breast cancer
• Non-Hodgkin lymphoma
• Ovarian cancer
• CLL (chronic lymphocytic leukemia)
• Neuroblastoma, Wilms tumor, rhabdomyosarcoma
• Also used as an immunosuppressant (lupus, nephrotic syndrome, vasculitis)

• Chlorambucil - oral, used for CLL and low-grade lymphomas
• Melphalan - used for multiple myeloma
• Mechlorethamine (mustine) - the original nitrogen mustard, used in MOPP regimen for Hodgkin lymphoma
• Bendamustine - hybrid molecule, used in CLL and non-Hodgkin lymphoma

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Subclass 2: Nitrosoureas

• Brain tumors (glioblastoma multiforme, astrocytoma)
• Hodgkin and non-Hodgkin lymphoma

• Delayed myelosuppression - The nadir (lowest blood count) occurs at 4-6 weeks after treatment (much later than other drugs where nadir is at 10-14 days)
• This delayed nadir is a frequently tested exam fact

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Subclass 3: Alkyl Sulfonates

• Chronic Myelogenous Leukemia (CML) - largely replaced by imatinib but still used in conditioning regimens before bone marrow transplant
• Pre-transplant conditioning regimens

• Pulmonary fibrosis ("busulfan lung") - interstitial fibrosis, very important to know
• Skin hyperpigmentation ("busulfan tan")
• Adrenal insufficiency
• Gonadal toxicity

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Subclass 4: Platinum Analogs (Cisplatin and Relatives)

• Testicular cancer (one of the curable cancers!)
• Bladder cancer
• Ovarian cancer
• Lung cancer (NSCLC, SCLC)
• Head and neck cancer
• Cervical cancer

• Carboplatin is less nephrotoxic and less emetogenic than cisplatin
• But carboplatin causes MORE myelosuppression
• Carboplatin is used when cisplatin's toxicity is unacceptable

• Used primarily in colorectal cancer (part of FOLFOX regimen)
• Unique toxicity: Cold-induced peripheral neuropathy - patients experience tingling/pain when touching cold objects or drinking cold liquids immediately after infusion (acute neuropathy - usually reversible)
• Also causes cumulative sensory neuropathy with continued dosing

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CLASS B - ANTIMETABOLITES

What Are They?

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Subclass 1: Antifolates

FOLATE PATHWAY (Simplified):

Dietary Folate
    ↓ Dihydrofolate reductase (DHFR) enzyme
Dihydrofolate (DHF)
    ↓ DHFR enzyme again
Tetrahydrofolate (THF) ← ACTIVE FORM
    ↓
Methylene-THF
    ↓ (with thymidylate synthase)
Makes THYMIDINE → Goes into DNA

Methotrexate enters cell
    ↓ 
Inhibits DIHYDROFOLATE REDUCTASE (DHFR) - the key enzyme
    ↓
DHF cannot be converted to THF
    ↓
No THF → No thymidine → No purines
    ↓
DNA synthesis stops
    ↓
Cell dies (especially rapidly dividing cells)

• Acute lymphoblastic leukemia (ALL) - backbone of treatment
• Osteosarcoma (bone cancer)
• Non-Hodgkin lymphoma
• Choriocarcinoma
• Head and neck cancers
• Non-cancer uses: Rheumatoid arthritis, psoriasis, inflammatory bowel disease, ectopic pregnancy (terminates ectopic pregnancy by killing rapidly dividing trophoblast cells)

• NSAIDs - reduce MTX excretion by kidneys → toxic levels
• Penicillins - reduce renal tubular secretion of MTX
• Proton pump inhibitors - some increase MTX levels
• Sulfonamides, trimethoprim - additive folate antagonism → worse toxicity

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Subclass 2: Pyrimidine Analogs

HOW 5-FU WORKS:

5-FU → converted inside cell to two active forms:
    
    ├── FdUMP (fluorodeoxyuridine monophosphate)
    │     ↓
    │   Inhibits THYMIDYLATE SYNTHASE
    │   (enzyme that makes thymidine for DNA)
    │   → "Thymineless death"
    │
    └── FUTP (fluorouridine triphosphate)
          ↓
        Incorporated into RNA → Disrupts RNA processing
        and protein synthesis

• Colorectal cancer (FOLFOX = 5-FU + leucovorin + oxaliplatin)
• Breast cancer
• Gastric cancer
• Pancreatic cancer
• Head and neck cancer
• Hepatocellular carcinoma

• Myelosuppression
• Mucositis/stomatitis
• Diarrhea
• Hand-foot syndrome (palmar-plantar erythrodysesthesia) - redness, blistering, pain on palms and soles - more common with infusional/oral 5-FU
• Cardiotoxicity - coronary vasospasm (especially with infusional 5-FU)
• Cerebellar ataxia (with high doses) - rare

• An oral prodrug of 5-FU
• Converted to 5-FU in tumor cells (by the enzyme thymidine phosphorylase, which is highly expressed in tumors)
• Used in breast and colorectal cancer
• Hand-foot syndrome is more prominent with capecitabine than IV 5-FU

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• A cytosine analog with arabinose sugar instead of ribose
• Incorporated into DNA, where it acts as a chain terminator (DNA polymerase can't continue past it)
• Also inhibits DNA polymerase directly
• Used primarily in acute myeloid leukemia (AML) - the backbone of AML induction therapy
• High-dose cytarabine (HiDAC) can cause cerebellar ataxia - one of its unique toxicities
• Also used in non-Hodgkin lymphoma

• Incorporated into DNA, inhibits DNA synthesis
• Used in: Pancreatic cancer (standard of care), non-small cell lung cancer (NSCLC), bladder cancer, breast cancer
• Well tolerated; main toxicities are myelosuppression and flu-like syndrome

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Subclass 3: Purine Analogs

• A purine analog that is incorporated into DNA and RNA, causing strand breaks
• Also inhibits de novo purine synthesis
• Used in ALL (leukemia) - maintenance therapy
• Metabolized by the enzyme xanthine oxidase to inactive metabolites
• Drug Interaction - CRITICAL: If given with allopurinol (a xanthine oxidase inhibitor used for gout or tumor lysis syndrome), 6-MP cannot be broken down and accumulates to toxic levels → SEVERE MYELOSUPPRESSION. Must reduce 6-MP dose by 75% if allopurinol is used concurrently.
• Metabolized by TPMT (thiopurine methyltransferase). Patients with low TPMT activity accumulate toxic levels.

• Similar to 6-MP; used in AML
• Less interaction with allopurinol than 6-MP

• A purine analog used in CLL (chronic lymphocytic leukemia) and indolent lymphomas
• Immunosuppressive - depletes T cells → risk of opportunistic infections

• Highly specific for lymphoid cells
• Drug of choice for hairy cell leukemia - a single 7-day continuous infusion often produces durable complete remission
• Also used in CLL and low-grade lymphomas

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CLASS C - NATURAL PRODUCT DRUGS

Subclass 1: Vinca Alkaloids

Vinca alkaloids
    ↓
Bind to TUBULIN (protein that makes microtubules)
    ↓
Prevent tubulin POLYMERIZATION
(prevent tubulin monomers from linking together)
    ↓
No microtubules form
    ↓
No MITOTIC SPINDLE can form
    ↓
Cell cannot separate its chromosomes
    ↓
Cell is arrested in METAPHASE (M phase)
    ↓
Cell death

"Vincristine = Neurotoxic (think: Neuro starts with N, and ViNCa = N for Neurotoxicity)" "VinBLastine = BLood (Bone marrow suppression)"

• Peripheral neuropathy - most common: loss of deep tendon reflexes (especially Achilles reflex - the first to go), then sensory neuropathy, then motor weakness
• Constipation - due to autonomic neuropathy affecting GI tract (can lead to paralytic ileus)
• SIADH - syndrome of inappropriate ADH secretion → hyponatremia
• Ptosis, diplopia (cranial nerve involvement)

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Subclass 2: Taxanes

Vinca alkaloids prevent microtubule FORMATION
BUT
Taxanes prevent microtubule DISASSEMBLY

Taxanes
    ↓
Bind to the β-tubulin subunit of microtubules
    ↓
STABILIZE microtubules (prevent depolymerization)
    ↓
Microtubules become frozen - can't break down
    ↓
Cell cannot complete mitosis (chromosomes can't separate properly)
    ↓
Cell is arrested in G2/M phase
    ↓
Cell death

• Breast cancer (first-line in metastatic)
• Ovarian cancer
• NSCLC (non-small cell lung cancer)
• Bladder cancer
• Kaposi sarcoma

• Peripheral neuropathy - dose-limiting toxicity (sensory)
• Myelosuppression (neutropenia)
• Hypersensitivity reactions - severe; due to the cremophor (solvent) used to dissolve the drug. Must premedicate with dexamethasone + H1 blocker + H2 blocker before each dose.
• Alopecia
• Bradycardia/heart block (cardiac arrhythmias) - uncommon but clinically significant

• Paclitaxel bound to albumin nanoparticles (no cremophor)
• Less hypersensitivity reactions
• Used in breast, pancreatic, lung cancer

• More potent than paclitaxel
• Unique toxicities: Fluid retention syndrome (edema, pleural effusions, ascites) - prevented with dexamethasone pretreatment; nail changes; more myelosuppression

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Subclass 3: Topoisomerase Inhibitors

• Topoisomerase I - cuts one strand of DNA, allows rotation, rejoins
• Topoisomerase II - cuts both strands of DNA, passes other DNA through, rejoins

• Irinotecan (CPT-11) - used in colorectal cancer (FOLFIRI regimen), lung cancer, cervical cancer
  • Active metabolite: SN-38 (converted by UGT1A1 enzyme in liver)
  • Key toxicity: SEVERE DIARRHEA (both acute cholinergic diarrhea immediately after infusion, and delayed secretory diarrhea 24-48 hours later)
  • Acute diarrhea treated with atropine; delayed diarrhea treated with loperamide
  • Patients with UGT1A1*28 polymorphism (reduced enzyme activity) are at HIGH risk for severe toxicity
• Topotecan - used in ovarian cancer, SCLC

• Etoposide (VP-16) - very commonly tested
  • Stabilizes the topoisomerase II-DNA complex (prevents DNA resealing) → double-strand breaks
  • Used in: Testicular cancer, SCLC, Hodgkin lymphoma, AML
  • Key toxicity: Secondary leukemia (AML) - can develop 2-3 years after treatment; associated with chromosomal translocation t(11q23)
  • Myelosuppression

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Subclass 4: Anti-Tumor Antibiotics

1. Intercalation into DNA
   (doxorubicin inserts itself between DNA base pairs like
   a crowbar forced between the rungs of a ladder - disrupts
   DNA structure and prevents transcription/replication)
   
2. Inhibition of Topoisomerase II
   (prevents DNA from being properly repaired after normal breaks)
   
3. Formation of free radicals
   (especially in heart tissue, where the free radicals cause
   direct membrane damage to cardiac muscle cells)

• Breast cancer (one of the most active drugs)
• Hodgkin lymphoma (ABVD regimen: doxorubicin + bleomycin + vinblastine + dacarbazine)
• Non-Hodgkin lymphoma (CHOP regimen: cyclophosphamide + doxorubicin + vincristine + prednisone)
• Soft tissue sarcoma
• Bladder cancer, ovarian cancer

• Doxorubicin causes direct damage to cardiac myocytes through free radical generation
• The heart has few antioxidant defenses (unlike other tissues)
• Cumulative dose is the key - risk rises significantly above 550 mg/m² cumulative dose
• Initially presents as dilated cardiomyopathy (the heart dilates and contracts poorly)
• Can progress to congestive heart failure
• Monitor with echocardiogram (ECHO) or MUGA scan before each cycle
• Irreversible once significant damage occurs

• Dexrazoxane - an iron chelator that reduces free radical formation in the heart. Used to prevent doxorubicin-induced cardiomyopathy when cumulative doses are high.
• Liposomal doxorubicin (Doxil) - encapsulation in liposomes reduces cardiac exposure.

• Severe myelosuppression
• Severe alopecia (very common)
• Red-colored urine (red pigment in drug) - patients must be warned to avoid panic
• Mucositis
• Vesicant - severe tissue damage if extravasation occurs

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Bleomycin
    ↓
Forms a complex with iron (Fe)
    ↓
Complex reacts with oxygen to generate FREE RADICALS
(specifically superoxide and hydroxyl radicals)
    ↓
Free radicals cause SINGLE AND DOUBLE-STRAND DNA BREAKS
    ↓
DNA cannot be repaired
    ↓
Cell dies

• It causes VERY LITTLE myelosuppression (compared to virtually all other anti-cancer drugs)
• This makes it invaluable in combination regimens where myelosuppression from other drugs already limits dosing

• Hodgkin lymphoma (ABVD regimen)
• Testicular/germ cell cancer (BEP regimen: bleomycin + etoposide + cisplatin) - CURABLE
• Squamous cell carcinomas (head and neck)

Bleomycin
    ↓
Free radicals also damage lung tissue
    ↓
Inflammatory response in lungs
    ↓
Progressive fibrosis (scarring) of lung parenchyma
    ↓
Restrictive lung disease
    ↓
Respiratory failure (in severe cases)

• Risk increases with cumulative dose above 450 units
• Risk also increased in patients who receive high concentrations of supplemental oxygen (oxygen fuels more free radical generation in the lung)
• During surgery, anesthesiologists must use the LOWEST possible FiO₂ in patients who have received bleomycin
• Monitor with pulmonary function tests (PFTs) - especially DLCO (carbon monoxide diffusion capacity)

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• Intercalates into DNA and inhibits RNA synthesis (RNA polymerase)
• Used in Wilms tumor (nephroblastoma) in children, gestational trophoblastic disease, Ewing sarcoma
• Part of a classic chemotherapy regimen VAC (vincristine + actinomycin D + cyclophosphamide)

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• Activated to form an alkylating agent inside cells
• DNA cross-linking
• Used in bladder cancer (intravesical instillation - delivered directly into bladder), gastric cancer

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Subclass 5: Miscellaneous Cytotoxic Drugs

• Inhibits ribonucleotide reductase - the enzyme that converts ribonucleoside diphosphates to deoxyribonucleoside diphosphates (the building blocks needed for DNA synthesis)
• S-phase specific
• Used in:
  • CML (mostly replaced by imatinib but still used)
  • Polycythemia vera, essential thrombocythemia
  • Sickle cell disease - increases production of fetal hemoglobin (HbF), which dilutes sickle hemoglobin and reduces crises. One of the most important non-oncologic uses.
• Toxicity: Myelosuppression, mucositis, skin ulcers, secondary leukemia with long-term use

• An enzyme that breaks down the amino acid asparagine
• Cancer cells (especially leukemia cells) cannot synthesize their own asparagine - they depend on external supply
• Normal cells CAN make their own asparagine
• L-Asparaginase depletes serum asparagine, starving cancer cells while sparing normal cells
• Used in: ALL (acute lymphoblastic leukemia)
• Toxicities:
  • Hypersensitivity/anaphylaxis (because it's a foreign bacterial protein - very common)
  • Pancreatitis (asparagine needed for pancreatic function)
  • Coagulopathy - inhibits synthesis of coagulation factors and fibrinogen
  • Hepatotoxicity
  • Neurotoxicity (drowsiness, confusion)
  • Notably: very little myelosuppression

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CLASS D - HORMONAL AGENTS

Estrogen-Related Drugs (for Breast Cancer)

• A Selective Estrogen Receptor Modulator (SERM) - acts as an estrogen ANTAGONIST in breast tissue but as an AGONIST in bone and uterus
• Binds to ER in breast cancer cells → blocks estrogen from binding → cancer cells get no growth signal → growth stops
• Used in ER-positive breast cancer - both treatment and prevention
• Metabolized to endoxifen (active metabolite) by CYP2D6
• Side effects:
  • Hot flashes (anti-estrogenic effect in hypothalamus)
  • Endometrial cancer - because it acts as estrogen agonist in uterus (increases endometrial cell proliferation)
  • Thromboembolic events (DVT, pulmonary embolism) - estrogen-like effect on clotting
  • Vaginal discharge/dryness
  • Eye toxicity - retinopathy and corneal changes (rare, with long-term use)

• A pure estrogen receptor antagonist (also called SERD - Selective Estrogen Receptor Degrader)
• Unlike tamoxifen, has NO agonist effects anywhere
• Binds to ER and also causes the receptor to be degraded
• Used in ER-positive metastatic breast cancer after tamoxifen failure
• Given as monthly intramuscular injection

• Drugs: Anastrozole, Letrozole, Exemestane
• Mechanism: In postmenopausal women, estrogen is no longer made by ovaries; it is made by conversion of androgens to estrogens in peripheral fat tissue by the enzyme aromatase. AIs block aromatase → less estrogen in the body → cancer starved of estrogen.
• Used only in postmenopausal women (or in premenopausal women if ovarian function is also suppressed)
• Side effects:
  • Osteoporosis/bone loss (because estrogen normally protects bones; reducing estrogen accelerates bone resorption)
  • Arthralgia/myalgia (joint and muscle aches) - very common
  • Hot flashes
  • No uterine cancer risk (unlike tamoxifen)
  • No thromboembolic risk (unlike tamoxifen)

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Androgen-Related Drugs (for Prostate Cancer)

• Drugs: Leuprolide, Goserelin, Buserelin, Triptorelin
• Normally, GnRH (from hypothalamus) is released in pulses → stimulates pituitary to release LH and FSH → LH stimulates testes to produce testosterone
• Continuous (non-pulsatile) GnRH agonist administration causes downregulation and desensitization of pituitary GnRH receptors → pituitary stops responding → LH/FSH fall → testes stop making testosterone → "medical castration"
• Initial "flare" phenomenon: When treatment first starts, there is a brief surge in testosterone before the receptors downregulate. This can worsen symptoms temporarily (bone pain flare in prostate cancer mets). To prevent this, an antiandrogen (flutamide or bicalutamide) is given for the first 2-4 weeks.
• GnRH Antagonists (Degarelix): Block GnRH receptors directly → NO initial flare; faster testosterone suppression

• Drugs: Flutamide, Bicalutamide, Enzalutamide
• Block androgen receptors directly - testosterone cannot bind and stimulate cancer cells
• Used in combination with GnRH agonists for "combined androgen blockade"

• Inhibits CYP17 (17α-hydroxylase/17,20-lyase) - an enzyme critical for androgen synthesis in the adrenal glands AND within the tumor itself
• Given with prednisone (to prevent adrenal insufficiency from androgen synthesis blockade)
• Used in castration-resistant prostate cancer

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CLASS E - TARGETED THERAPIES

Tyrosine Kinase Inhibitors (TKIs)

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• Almost all CML is caused by a specific chromosomal abnormality: the Philadelphia chromosome (Ph)
• The t(9;22) translocation - part of chromosome 9 (containing the ABL oncogene) swaps with part of chromosome 22 (containing the BCR gene)
• This creates the BCR-ABL fusion gene on chromosome 22
• The BCR-ABL fusion protein is a constitutively active (always ON) tyrosine kinase
• This permanently tells cells to divide → CML

Philadelphia Chromosome:
Normal chromosome 9:  ...ABL...
Normal chromosome 22: ...BCR...
           ↓ Translocation t(9;22)
Chromosome 22 (now shortened = "Philadelphia chromosome"):
...BCR-ABL fusion gene...
           ↓
BCR-ABL fusion protein = Constitutively active tyrosine kinase
           ↓
CONSTANT CELL DIVISION → CML

• Imatinib binds specifically to the ATP-binding site of the BCR-ABL tyrosine kinase
• It blocks ATP from binding → tyrosine kinase cannot be activated → the "always ON" switch is turned OFF
• Without the survival signal, CML cells die

• c-kit (CD117) - a tyrosine kinase receptor on GIST (gastrointestinal stromal tumors). ~80% of GISTs have activating mutations in c-kit. Imatinib is therefore also used for GIST.
• PDGFR (platelet-derived growth factor receptor)

• Nausea, vomiting, diarrhea
• Edema/fluid retention (especially periorbital edema)
• Muscle cramps
• Skin rash
• Myelosuppression (mild)
• Hepatotoxicity (rare)

• The most common mechanism is a T315I mutation ("gatekeeper mutation") in the BCR-ABL kinase domain - this mutation prevents imatinib from binding
• Second-generation TKIs (dasatinib, nilotinib, bosutinib) overcome most resistance mutations EXCEPT T315I
• Ponatinib (third-generation) is the only drug that inhibits T315I

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• Gefitinib, Erlotinib (1st generation) - inhibit EGFR; used for EGFR-mutant NSCLC
• Afatinib (2nd generation) - irreversible EGFR inhibitor
• Osimertinib (Tagrisso) (3rd generation) - active against T790M resistance mutation in EGFR; also first-line for EGFR-mutant NSCLC

• Acneiform rash (papulopustular rash on face and trunk) - paradoxically, a worse rash correlates with better drug response
• Diarrhea
• Dry skin
• Hepatotoxicity
• Interstitial lung disease (rare but serious)

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Monoclonal Antibodies

• All end in "-mab" (monoclonal antibody)
• "-zu-" or "-u-" in the name = humanized or fully human (less immunogenic)
• "-xi-" = chimeric (part mouse, part human)

• Target: HER2 (Human Epidermal Growth Factor Receptor 2) - overexpressed in ~20-25% of breast cancers
• Mechanism: Binds to HER2 → prevents HER2 dimerization and signaling → inhibits cell proliferation; also triggers ADCC (antibody-dependent cellular cytotoxicity) - immune cells destroy HER2-positive cancer cells
• Used in HER2-positive breast cancer and HER2-positive gastric cancer
• Major toxicity: Cardiotoxicity - causes reversible cardiomyopathy (unlike doxorubicin which is irreversible). Monitor with ECHO. Do not use with anthracyclines simultaneously due to additive cardiotoxicity.

• Target: CD20 - present on all mature B cells and most B-cell lymphomas/leukemias
• Mechanism: Binds CD20 → triggers complement-mediated cytolysis + ADCC → B cells are destroyed
• Used in: B-cell non-Hodgkin lymphoma, CLL, diffuse large B-cell lymphoma
• Also used in: Rheumatoid arthritis, autoimmune diseases (off-label)
• Side effects: Infusion reactions (fever, chills, hypotension during first infusion), B-cell depletion → increased infection risk, rare hepatitis B reactivation, rare progressive multifocal leukoencephalopathy (PML - due to JC virus reactivation)

• Target: VEGF (Vascular Endothelial Growth Factor) - the signaling protein that tells the body to grow new blood vessels
• Mechanism: Binds and neutralizes VEGF → no new blood vessel formation (anti-angiogenic) → tumor cannot get its blood supply → tumor growth is restricted
• Used in: Colorectal cancer, NSCLC, renal cell carcinoma, glioblastoma, ovarian cancer, cervical cancer
• Unique toxicities:
  • Hypertension (VEGF normally keeps blood vessels dilated; blocking it causes vasoconstriction)
  • Impaired wound healing (blood vessel growth needed for healing)
  • Thromboembolism (arterial thrombosis, DVT, PE)
  • GI perforation (very important! Contraindicated immediately before/after surgery)
  • Bleeding/hemorrhage
  • Proteinuria

• Target: EGFR (Epidermal Growth Factor Receptor) - a receptor on cell surfaces
• Mechanism: Binds to the extracellular domain of EGFR → blocks EGF from binding → no growth signal
• Used in: Colorectal cancer (but ONLY if the tumor has wild-type KRAS - if KRAS is mutated, the downstream pathway is constitutively active and blocking EGFR has no effect) and head and neck cancer
• Testing for KRAS mutation is mandatory before giving cetuximab

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Immune Checkpoint Inhibitors

NORMAL CHECKPOINT MECHANISM:
T cell encounters cancer cell
    ↓
T cell wants to attack
    ↓
Cancer cell presents PD-L1 protein
(like showing a "diplomatic immunity" card)
    ↓
T cell's PD-1 receptor binds to PD-L1
    ↓
T cell is inactivated/exhausted
    ↓
Cancer cell escapes
    
CHECKPOINT INHIBITOR MECHANISM:
Pembrolizumab (anti-PD-1 antibody) blocks PD-1 on T cell
OR
Atezolizumab (anti-PD-L1 antibody) blocks PD-L1 on cancer cell
    ↓
T cell is no longer inactivated
    ↓
T cell attacks and kills cancer cell

1. PD-1/PD-L1 pathway:
   • PD-1 = Programmed Death 1 (on T cells)
   • PD-L1 = Programmed Death Ligand 1 (on cancer cells/other cells)
   • Anti-PD-1 drugs: Pembrolizumab (Keytruda), Nivolumab (Opdivo)
   • Anti-PD-L1 drugs: Atezolizumab, Durvalumab, Avelumab
2. CTLA-4 pathway:
   • CTLA-4 = Cytotoxic T-Lymphocyte-Associated protein 4 (on T cells - an earlier, more fundamental brake)
   • Anti-CTLA-4: Ipilimumab (Yervoy)

• Melanoma (ipilimumab + nivolumab = very effective combination)
• NSCLC
• Renal cell carcinoma
• Hodgkin lymphoma (nivolumab)
• Bladder cancer
• MSI-high tumors (any cancer with high microsatellite instability - biomarker for checkpoint inhibitor response)
• Hepatocellular carcinoma
• Head and neck cancer

1. Grade 1-2: Continue drug, manage symptomatically
2. Grade 3: Hold drug, start high-dose corticosteroids
3. Grade 4: Permanently discontinue drug, high-dose corticosteroids
4. Use infliximab (anti-TNF) for steroid-refractory colitis

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CLASS F - PARP INHIBITORS

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SECTION 4: TEACH USING ANALOGIES

The Master Analogy Set

The cancer cell's DNA is like a blueprint for building weapons. Alkylating agents sneak into the factory (the cell) and scribble all over the blueprint, gluing pages together. The factory workers (DNA polymerase) pick up the blueprint to copy it, but the pages are stuck together and unreadable. The factory shuts down.

The cell needs specific building blocks to make DNA - think of them as special coins needed to run the DNA-copying machine. Antimetabolites are counterfeit coins that look exactly right but jam the machine. The machine accepts them, then jams and stops working. The cell can't copy its DNA.

Methotrexate is like cutting off the supply of a crucial raw material. The cell needs folate to make thymidine. Methotrexate blocks the factory that processes folate into usable form. Without thymidine, the DNA copying machine has no "T" blocks to use. Production stops.

When a cell divides, it uses microscopic cranes (spindle fibers made of tubulin) to pull chromosomes to either end of the cell before division. Vinca alkaloids prevent the crane from being built. Without the crane, chromosomes pile up in the middle and can't be separated. Division fails.

While vinca alkaloids prevent the crane from being assembled, taxanes super-glue the crane permanently. It can't be disassembled when needed. The crane is stuck in place - the cell is paralyzed mid-division.

DNA is like a library of genetic instruction books. To make proteins or copy DNA, the books must be opened. Doxorubicin jams itself physically between the pages of the books (intercalation), AND breaks the chains holding the books on the shelves (topoisomerase II inhibition). The library is destroyed. Unfortunately, the drug also generates sparks (free radicals) that set the heart tissue on fire.

CML cancer cells have a permanently jammed accelerator (BCR-ABL tyrosine kinase). Normal cells don't have this specific accelerator. Imatinib is like a tiny key that fits only into this specific jammed accelerator and disables it. The cancer cells lose their driving force and die. Normal cells are unaffected because they don't have this abnormal accelerator.

Tumors are like cities that need water (blood supply) to survive. They call for new water pipes to be built (VEGF signals for angiogenesis). Bevacizumab intercepts the "build water pipes" message and blocks it. The tumor cannot get its water supply. Growth is restricted.

Your T cells (immune fighters) are like attack dogs on leashes. Cancer cells have put a special muzzle on these dogs using PD-L1 (showing the dogs a fake "friend" ID card). Checkpoint inhibitors rip the muzzle off. Now the attack dogs can recognize and attack the cancer cells freely. The downside: without the muzzle, the dogs may also bite friendly tissues (autoimmune side effects).

Leukemia cells cannot make their own asparagine (an amino acid they need to survive) - they must get it from the blood. Normal cells can make their own asparagine. L-Asparaginase destroys all circulating asparagine. Normal cells shrug and make their own. Leukemia cells starve.

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SECTION 5: STEP-BY-STEP CLINICAL REASONING

Case 1: Newly Diagnosed CML

• BCR-ABL PCR quantification in blood every 3 months
• Target: "Major Molecular Response" (BCR-ABL ratio < 0.1%) by 12 months
• Complete cytogenetic response (no Philadelphia chromosome detectable) by 12 months

• Check for BCR-ABL kinase domain mutations
• If T315I mutation: switch to ponatinib
• If other mutations: switch to alternative second-generation TKI

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Case 2: Newly Diagnosed Metastatic Colorectal Cancer

1. Cytotoxic backbone: FOLFOX (5-FU + leucovorin + oxaliplatin) or FOLFIRI (5-FU + leucovorin + irinotecan)
2. Add targeted therapy: KRAS wild-type → can add cetuximab (anti-EGFR) OR bevacizumab (anti-VEGF)
   • If KRAS mutated: CANNOT use cetuximab; use bevacizumab
3. Biomarker testing:
   • Test for DPD deficiency (before starting 5-FU) - severe toxicity if deficient
   • Test for UGT1A1*28 (if using irinotecan) - severe diarrhea if poor metabolizer
   • Test for MSI status - if MSI-high: checkpoint inhibitors (pembrolizumab) are highly effective as first-line therapy
4. Monitoring:
   • CEA tumor marker
   • CT scan every 2-3 cycles
   • Toxicity monitoring: complete blood count (myelosuppression), peripheral neuropathy assessment (oxaliplatin), diarrhea management (irinotecan)

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Case 3: Breast Cancer in a 40-year-old Premenopausal Woman

1. Surgery first (usually mastectomy or lumpectomy + radiation)
2. Adjuvant chemotherapy: Node-positive = high risk → offer chemotherapy
   • Standard regimen: AC-T (doxorubicin + cyclophosphamide → paclitaxel)
   • Monitor cardiac function (doxorubicin)
3. Endocrine therapy (5-10 years):
   • Premenopausal → Tamoxifen for 5-10 years
   • OR ovarian suppression (leuprolide/goserelin) + aromatase inhibitor
4. Concerns:
   • Doxorubicin: monitor ECHO for cardiac function
   • Cyclophosphamide: hemorrhagic cystitis (prevent with hydration)
   • Paclitaxel: peripheral neuropathy, hypersensitivity reactions (premedicate)
   • Tamoxifen: risk of endometrial cancer - annual gynecologic review; DVT/PE risk

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SECTION 6: MEMORY TOOLS

Key Mnemonics

Alkylating agents Antimetabolites Anti-tumor antibiotics Natural products (vinca, taxanes, etoposide) Newer targeted therapies (TKIs, MAbs, checkpoint inhibitors) Hormonal agents Hydroxyurea & misc.

"Vincristine hits the Nerves (N in the middle), Vinblastine hits the Blood (B)" VinCriStine → Cranial nerves, Constipation, Cramps (neurological) VinBlastine → Bone marrow (myelosuppression)

Cardiotoxicity (rare, but nausea is severe) Ototoxicity (hearing loss, irreversible) Nephrotoxicity (most important dose-limiting toxicity) Knee/limb neuropathy (peripheral neuropathy)

"Cyclo = Cyclo-phosphamide goes to the BLADDER → hemorrhagic CYSTITIS" Mesna M.E.S.N.A. = Makes Enough Safety from Nasty Acrolein

"B-CAMP" Bleomycin Carmustine (nitrosourea) Amytryptline? No... Amiodarone (non-cancer) Methotrexate (lung toxicity too) Busulfan (Pulmonary fibrosis in situ)

"DaDa Cyc T" Doxorubicin (anthracyclines) Daunorubicin Cyclophosphamide (high-dose) Trastuzumab

FOL = Leucovorin (FOLate derivative) F = 5-Fluorouracil (5-FU) OX = OXaliplatin

A = doxorubicin (Adriamycin) B = Bleomycin V = Vinblastine D = Dacarbazine

C = Cyclophosphamide H = doxorubicin (Hydroxydaunorubicin = Adriamycin) O = vincristine (Oncovin) P = Prednisolone

B = Bleomycin E = Etoposide P = Cisplatin (Platinum)

S-phase specific: Antimetabolites (MTX, 5-FU, cytarabine, gemcitabine) M-phase specific: Vinca alkaloids G2/M-phase specific: Taxanes, bleomycin Non-cell-cycle specific (all phases): Alkylating agents, platinum drugs, anthracyclines

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Drug Comparison Tables

Table 1: Complete Alkylating Agents Overview

Table 2: Complete Antimetabolite Overview

Table 3: Natural Product Drugs

Table 4: Targeted Therapies

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SECTION 7: EXAMINER'S CORNER

Most Tested Facts (High-Yield Exam Pearls)

Drug-Toxicity Pairs (Most Tested)

1. Doxorubicin → Dilated cardiomyopathy (dose-dependent, cumulative; limit: 550 mg/m²; monitor with ECHO)
2. Bleomycin → Pulmonary fibrosis (avoid high FiO₂ during surgery)
3. Cisplatin → Nephrotoxicity + Ototoxicity (dose-limiting = nephrotoxicity)
4. Cyclophosphamide → Hemorrhagic cystitis (prevented by mesna + hydration)
5. Vincristine → Neurotoxicity (peripheral neuropathy, constipation) + minimal myelosuppression
6. Busulfan → Pulmonary fibrosis + Skin hyperpigmentation
7. Methotrexate → Hepatotoxicity + nephrotoxicity + mucositis (leucovorin rescue)
8. Nitrosoureas (Carmustine/Lomustine) → Delayed myelosuppression at 4-6 weeks
9. Tamoxifen → Endometrial cancer + DVT/PE
10. L-Asparaginase → Pancreatitis + coagulopathy + hypersensitivity (no myelosuppression)

Drug-Use Pairs (Most Tested)

1. Imatinib → CML (BCR-ABL) + GIST (c-kit)
2. Rituximab → B-cell lymphoma + CLL (CD20)
3. Trastuzumab → HER2+ breast cancer
4. Bevacizumab → Anti-angiogenic (VEGF) + colorectal, renal cell carcinoma
5. Cladribine → Hairy cell leukemia (drug of choice)
6. L-Asparaginase → ALL (acute lymphoblastic leukemia)
7. Cytarabine (Ara-C) → AML (acute myeloid leukemia)
8. Carmustine → Brain tumors (crosses blood-brain barrier)
9. Bleomycin → Testicular cancer (BEP) + Hodgkin lymphoma (ABVD)
10. Tamoxifen → ER-positive premenopausal breast cancer

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Most Likely Essay Questions

1. "Classify anti-cancer drugs with mechanism of action and important side effects." (The most classic essay)
2. "Describe the mechanism of action, clinical uses, and adverse effects of cisplatin."
3. "Discuss the pharmacology of methotrexate including its mechanism, uses, toxicity, and drug interactions."
4. "Write a note on targeted therapy in cancer with examples."
5. "Describe the mechanism of resistance to anti-cancer drugs."
6. "Write a note on immune checkpoint inhibitors."
7. "Discuss hormonal therapy in breast cancer."

Most Likely Short Notes

1. Hemorrhagic cystitis and its prevention
2. Cardiotoxicity of doxorubicin
3. Pulmonary toxicity of bleomycin
4. Leucovorin rescue
5. Imatinib in CML
6. Philadelphia chromosome
7. Tamoxifen
8. L-Asparaginase
9. Vincristine vs Vinblastine
10. Tumor lysis syndrome

Most Likely Viva Questions

• "What is the mechanism of cisplatin?"
• "Name one drug that causes pulmonary fibrosis."
• "What is the antidote for methotrexate toxicity?"
• "What is mesna and why is it used?"
• "Name the drug of choice for hairy cell leukemia."
• "What is the BCR-ABL gene and which drug targets it?"
• "What is the mechanism of taxanes vs vinca alkaloids?"
• "Why does bleomycin spare bone marrow?"
• "What is the dose-limiting toxicity of cisplatin?"
• "What is leucovorin rescue?"

Common MCQ Patterns

"A patient develops hematuria after chemotherapy. Which drug is most likely responsible?" → Cyclophosphamide

"Which drug prevents tubulin polymerization?" → Vincristine / Vinblastine (not taxanes - those stabilize microtubules)

"Drug of choice for hairy cell leukemia?" → Cladribine "Drug of choice for CML?" → Imatinib (or any BCR-ABL TKI)

"Which drug interaction can cause fatal toxicity with 6-mercaptopurine?" → Allopurinol (inhibits xanthine oxidase, which metabolizes 6-MP → 6-MP accumulates to toxic levels)

"Which drug is absolutely contraindicated in pregnancy?" → Methotrexate (and most cytotoxic drugs) "Which chemo drug requires DPD testing before use?" → 5-Fluorouracil / Capecitabine

"Which drug acts only in S phase of cell cycle?" → Antimetabolites (methotrexate, 5-FU, cytarabine)

Traps Students Fall Into

1. Confusing Vincristine and Vinblastine toxicities - the single most common viva trap. Always: Vincristine → Neuro; Vinblastine → Blood.
2. Saying doxorubicin cardiomyopathy is reversible - it is NOT. Trastuzumab cardiotoxicity IS reversible. Know this distinction.
3. Forgetting that cisplatin nephrotoxicity is dose-LIMITING but ototoxicity is irreversible and not dose-limiting (dose-related but not dose-limiting).
4. Confusing "leucovorin rescue" in methotrexate toxicity with "leucovorin enhancement" in 5-FU. With MTX: leucovorin rescues NORMAL cells. With 5-FU: leucovorin ENHANCES anti-cancer activity.
5. Forgetting the allopurinol + 6-MP interaction - a classic high-stakes drug interaction.
6. Saying bleomycin causes myelosuppression - it is famous for causing very LITTLE myelosuppression. This is why it is so useful in combination regimens.
7. Not knowing that taxanes STABILIZE microtubules (they do NOT destroy them) - many students say taxanes work by the same mechanism as vinca alkaloids.
8. Forgetting that cetuximab requires KRAS testing - a major clinical and exam point.
9. Confusing nitrosourea delayed myelosuppression nadir (4-6 weeks) with other drugs (10-14 days).
10. Forgetting that L-asparaginase causes coagulopathy by reducing fibrinogen and coagulation factors - not just hypersensitivity and pancreatitis.

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SECTION 9: HIGH-YIELD REVISION SHEET

╔══════════════════════════════════════════════════════════════════╗
║           ANTI-CANCER DRUGS - ONE-PAGE REVISION SHEET           ║
╠══════════════════════════════════════════════════════════════════╣
║                                                                   ║
║  ALKYLATING AGENTS (NON-CELL-CYCLE SPECIFIC)                     ║
║  • Cyclophosphamide → Hemorrhagic cystitis (prevent: mesna)      ║
║  • Busulfan → Pulmonary fibrosis + skin hyperpigmentation        ║
║  • Carmustine → Brain tumors (crosses BBB); delayed myelo        ║
║  • Cisplatin → Nephrotoxicity (dose-limiting) + Ototoxicity      ║
║  • Carboplatin → More myelosuppression, less nephrotoxic         ║
║  • Oxaliplatin → Colorectal (FOLFOX); cold neuropathy            ║
║                                                                   ║
║  ANTIMETABOLITES (S-PHASE SPECIFIC)                              ║
║  • Methotrexate → DHFR inhibitor; rescue = LEUCOVORIN            ║
║    Toxicity: hepatic, renal, mucositis; TERATOGEN                ║
║    Interaction: NSAIDs ↑ MTX toxicity                            ║
║  • 5-FU → Thymidylate synthase inhibitor; hand-foot syndrome     ║
║    DPD deficiency = severe life-threatening toxicity             ║
║    Leucovorin ENHANCES 5-FU (not rescues)                        ║
║  • Cytarabine → AML; HiDAC → cerebellar ataxia                   ║
║  • 6-MP → ALL; +Allopurinol = FATAL (reduce dose 75%)           ║
║  • Cladribine → Hairy cell leukemia (DOC)                        ║
║                                                                   ║
║  NATURAL PRODUCTS                                                 ║
║  • Vincristine → Neurotoxicity (NO myelosuppression)             ║
║  • Vinblastine → Myelosuppression                                ║
║  • Paclitaxel → Peripheral neuropathy; hypersensitivity          ║
║    (premedicate); stabilizes microtubules                         ║
║  • Doxorubicin → Dilated cardiomyopathy (cumulative, dose-dep)   ║
║    Limit: 550 mg/m²; Monitor ECHO; RED URINE                     ║
║    Protection: Dexrazoxane                                        ║
║  • Bleomycin → Pulmonary fibrosis; NO myelosuppression           ║
║    Avoid high FiO₂ during surgery!                               ║
║  • Etoposide → Secondary AML (Topo II inhibitor)                 ║
║  • Irinotecan → Severe diarrhea; check UGT1A1 polymorphism       ║
║                                                                   ║
║  HORMONAL AGENTS                                                  ║
║  • Tamoxifen → ER+ breast Ca; endometrial Ca + DVT risk          ║
║  • Aromatase inhibitors → Postmenopausal; osteoporosis           ║
║  • Leuprolide → Prostate Ca; initial flare (give antiandrogen)   ║
║                                                                   ║
║  TARGETED THERAPIES                                               ║
║  • Imatinib → CML (BCR-ABL) + GIST (c-kit) → minimal toxicity   ║
║  • Trastuzumab → HER2+ breast Ca → REVERSIBLE cardiomyopathy    ║
║  • Rituximab → CD20+ lymphomas → Infusion reactions              ║
║  • Bevacizumab → VEGF → Hypertension, GI perforation, bleeding  ║
║  • Cetuximab → KRAS wild-type required; EGFR (colorectal)        ║
║  • Pembrolizumab → PD-1; immune-related AEs (colitis, pneumo)    ║
║  • Olaparib → PARP; BRCA-mutated cancers                         ║
║                                                                   ║
║  IMPORTANT COMBINATIONS                                           ║
║  • ABVD = Doxorubicin + Bleomycin + Vinblastine + Dacarbazine    ║
║    (Hodgkin lymphoma)                                             ║
║  • CHOP = Cyclophosphamide + doxorubicin + Vincristine + Pred    ║
║    (B-cell NHL; + rituximab = R-CHOP)                            ║
║  • BEP = Bleomycin + Etoposide + Cisplatin (testicular - CURES)  ║
║  • FOLFOX = 5-FU + Leucovorin + Oxaliplatin (colorectal)         ║
║  • FOLFIRI = 5-FU + Leucovorin + Irinotecan (colorectal)         ║
║                                                                   ║
║  MUST-KNOW MECHANISMS OF RESISTANCE                               ║
║  • MDR1 (P-glycoprotein overexpression) → pumps drug out         ║
║  • Gene amplification (e.g., DHFR) → more target protein         ║
║  • Reduced drug uptake                                            ║
║  • Mutations in drug target (e.g., T315I in BCR-ABL)             ║
║  • Enhanced DNA repair                                            ║
║  • Altered apoptotic pathways (BCL-2 overexpression)             ║
╚══════════════════════════════════════════════════════════════════╝

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SECTION 10: SELF-ASSESSMENT - 10 Questions

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• Monitor ECHO/MUGA scan before each cycle; stop if EF falls significantly
• Limit cumulative dose to < 550 mg/m² (< 450 mg/m² if prior mediastinal radiation)
• Use dexrazoxane (iron chelator) at high cumulative doses to reduce free radical formation
• Use liposomal doxorubicin (Doxil/Caelyx) which has better cardiac sparing
• Unlike trastuzumab-induced cardiomyopathy, doxorubicin cardiac toxicity is largely irreversible

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1. Removes a hydrogen bond that imatinib relies on for binding
2. Adds a bulky isoleucine residue that sterically blocks imatinib from entering the ATP-binding pocket

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• The lung parenchyma has reduced antioxidant reserves (already consumed by prior drug-induced oxidative stress)
• High intraoperative FiO₂ can precipitate acute pulmonary decompensation or worsen pre-existing fibrosis
• Even if the patient appears normal on PFTs, the lung may be sensitized

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• DEXA scan (bone mineral density) at baseline and annually - prescribe calcium + vitamin D + bisphosphonate if bone density is poor
• Lipid profile (some impact on lipids)
• Regular follow-up for arthralgia (can lead to poor adherence)
• No gynecologic monitoring needed (no endometrial risk)

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• After cycle 1: 10⁷ cells (99.9% killed)
• After cycle 2: 10⁴ cells
• After cycle 3: 10¹ cells (potentially curable)

1. Progressively reduce tumor burden to undetectable levels
2. Allow some normal tissue recovery between cycles (normal cells recover faster than cancer cells due to greater regenerative capacity)
3. Reduce the risk of resistance emerging from surviving subclones

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• Normal cells: Unaffected (make their own)
• Leukemia cells: Deprived of essential asparagine → protein synthesis fails → cell dies

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EGFR (receptor)
    ↓
KRAS (signaling relay, RAS)
    ↓
RAF → MEK → ERK
    ↓
Cell proliferation

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• GI: Colitis (diarrhea, bloody stool)
• Liver: Hepatitis (raised transaminases)
• Lung: Pneumonitis (cough, dyspnea, infiltrates on CT)
• Endocrine: Hypothyroidism, hyperthyroidism, hypophysitis (pituitary inflammation), adrenal insufficiency, Type 1 diabetes
• Skin: Rash, vitiligo, pruritis
• Kidney: Nephritis

• Grade 1 (mild): Continue checkpoint inhibitor; symptomatic management
• Grade 2 (moderate): Hold checkpoint inhibitor; start oral prednisone ~1 mg/kg/day; monitor closely
• Grade 3 (severe): Permanently discontinue in most cases; start IV methylprednisolone 1-2 mg/kg/day
• Grade 4 (life-threatening): Permanently discontinue; high-dose IV steroids; ICU if needed
• Steroid-refractory colitis/hepatitis: Add infliximab (anti-TNF) for colitis; mycophenolate for hepatitis

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• Renal function is impaired (MTX itself can cause tubular damage)
• Inadequate hydration leads to MTX precipitation in renal tubules
• Certain drugs (NSAIDs, penicillins) reduce renal MTX secretion

1. Leucovorin (folinic acid) rescue - administer IV leucovorin at doses high enough to compete with MTX in normal tissues. Leucovorin bypasses the blocked DHFR enzyme (it is already in the reduced form, not needing DHFR processing). This rescues normal cells from MTX toxicity.
   • Doses must be matched to MTX levels; continue until MTX level falls to safe range
2. Aggressive IV hydration to promote MTX excretion
3. Urine alkalinization (sodium bicarbonate) - MTX is more soluble at alkaline pH, reducing crystallization in tubules
4. Glucarpidase (carboxypeptidase G2) - a rescue enzyme that directly cleaves MTX into inactive metabolites; used in severe cases with very high MTX levels when leucovorin alone is insufficient
5. Close monitoring of renal function, blood counts, MTX levels until resolved

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