2nd MBBS Pathology - MUHS Exam Notes

TOPIC 1: FATTY LIVER - ETIOPATHOGENESIS

Definition

Classification / Etiology

FATTY LIVER
├── ALCOHOLIC
│   └── Most common cause worldwide
│       - Ethanol → acetaldehyde
│       - Increases NADH / NAD+ ratio
│       - Inhibits beta-oxidation of fatty acids
│       - Increases fatty acid synthesis
│       - Blocks VLDL secretion
│
└── NON-ALCOHOLIC (NAFLD)
    ├── Type 2 diabetes mellitus
    ├── Obesity (especially central)
    ├── Dyslipidemia
    ├── Hypertension
    ├── Metabolic syndrome
    └── Also: starvation, protein deficiency,
        drugs (corticosteroids, methotrexate),
        pregnancy (acute fatty liver of pregnancy)

Pathogenesis of Fatty Liver

Mechanisms of Fat Accumulation in Hepatocytes:

┌─────────────────────────────────────────────────────────────┐
│              NORMAL HEPATOCYTE FAT BALANCE                  │
│                                                             │
│  INPUT:  Free Fatty Acids (FFA) from adipose & diet         │
│          + De novo synthesis of FFA in liver                │
│                                                             │
│  OUTPUT: Beta-oxidation (mitochondria)                      │
│          + VLDL secretion into blood                        │
└─────────────────────────────────────────────────────────────┘

IMBALANCE → FAT ACCUMULATES

6 KEY MECHANISMS (Harsh Mohan Mnemonic: "DIVINE"):
1. Delivery↑  — Excess FFA delivery to liver (obesity, starvation)
2. Insulin resistance → ↑lipolysis from adipocytes → ↑FFA
3. Vitamin deficiency (choline/methionine) → ↓phospholipid synthesis → ↓VLDL
4. Inhibition of mitochondrial beta-oxidation (ethanol, hypoxia, toxins)
5. No VLDL export (liver toxins block apoprotein synthesis/secretion)
6. Excess synthesis of triglycerides (ethanol → ↑NADH)

Alcoholic Fatty Liver Pathogenesis (detailed):

• Ethanol → Acetaldehyde via alcohol dehydrogenase
• Generates excess NADH → shifts metabolism
• NADH↑ → Inhibits fatty acid oxidation (requires NAD+)
• NADH↑ → Promotes triglyceride synthesis
• Acetaldehyde → damages mitochondria → further blocks beta-oxidation
• Alcohol → impairs tubulin polymerization → traps VLDL inside hepatocyte

NAFLD Pathogenesis ("Two-Hit Hypothesis"):

• 1st Hit: Insulin resistance → ↑FFA uptake by liver → steatosis
• 2nd Hit: Oxidative stress, inflammasome activation (IL-1), lipotoxicity, gut-derived endotoxins → NASH (Nonalcoholic Steatohepatitis)

Morphology of Fatty Liver

Gross:

┌─────────────────────────────────────────┐
│  GROSS APPEARANCE OF FATTY LIVER        │
│                                         │
│  Size:   Enlarged (up to 3-6 kg)        │
│  Color:  Yellow (due to lipid)          │
│  Texture: Soft, greasy surface          │
│  Edge:   Rounded edges                  │
│  Cut section: Yellow, greasy, floats    │
│              in water (low density)     │
└─────────────────────────────────────────┘

Histopathology:

┌────────────────────────────────────────────────┐
│  HISTOLOGY OF FATTY LIVER                      │
│                                                │
│  • Large cytoplasmic vacuoles of fat           │
│  • Nucleus pushed to periphery (signet ring    │
│    appearance)  ← MACROVESICULAR (alcohol,     │
│                   obesity, diabetes)           │
│  • Small multiple vacuoles, central nucleus    │
│    → MICROVESICULAR (acute fatty liver of      │
│      pregnancy, Reye's syndrome, tetracycline) │
│  • Centrilobular distribution (alcoholic)      │
│  • Periportal distribution (severe cases)      │
│  • Mallory hyaline bodies (alcoholic)          │
│  • Neutrophilic infiltration (NASH)            │
│  • Special stain: Oil Red O / Sudan IV         │
│    (on frozen section - lipid washes in        │
│    routine processing)                         │
└────────────────────────────────────────────────┘

Exam Tip: Lipid dissolves in alcohol-xylene processing - must use frozen sections or Sudan stains to demonstrate fat histologically.

TOPIC 2A: CLASSIFICATION OF PIGMENTS

Pigments = colored substances in tissues

┌─────────────────────────────────────────────────────────────┐
│                  CLASSIFICATION OF PIGMENTS                 │
│                                                             │
│  EXOGENOUS (from outside body)                              │
│  ├── Carbon/Coal dust → Anthracosis (lungs, lymph nodes)    │
│  ├── Tattoo pigments (cinnabar, india ink)                  │
│  ├── Lead → bluish lines in gums (Burton's line)            │
│  ├── Silver → Argyria (grey-blue discoloration)             │
│  └── Asbestos → Ferruginous bodies                         │
│                                                             │
│  ENDOGENOUS (made by body)                                  │
│  ├── HEMOGLOBIN-DERIVED                                     │
│  │   ├── Hemosiderin (iron-containing, yellow-brown)        │
│  │   ├── Bilirubin (bile pigment - jaundice)                │
│  │   ├── Hematin (acid hematin / malaria pigment)           │
│  │   ├── Porphyrins                                         │
│  │   └── Hematoidin (bilirubin without iron)                │
│  │                                                          │
│  ├── NON-HEMOGLOBIN-DERIVED                                 │
│  │   ├── Melanin (brown-black, tyrosine-derived)            │
│  │   ├── Lipofuscin / Lipochrome ("wear-and-tear" pigment)  │
│  │   └── Chromaffin pigment (adrenal medulla)               │
└─────────────────────────────────────────────────────────────┘

Disorders of Melanin Pigmentation

MELANIN - Key Facts

• Synthesized by melanocytes in basal layer of epidermis
• Precursor: Tyrosine → DOPA → Dopaquinone → Melanin
• Enzyme: Tyrosinase
• Stored in melanosomes
• Transferred to keratinocytes

INCREASED MELANIN PIGMENTATION (Hypermelanosis/Hyperpigmentation)

┌────────────────────────────────────────────────────────┐
│          HYPERPIGMENTATION - CAUSES                    │
├─────────────────────┬──────────────────────────────────┤
│ Generalized         │ Addison's disease (↑ACTH/MSH)    │
│                     │ Hemochromatosis                  │
│                     │ Cachexia/malignancy              │
├─────────────────────┼──────────────────────────────────┤
│ Localized           │ Freckles (Ephilides)              │
│                     │ Melasma (Chloasma - pregnancy)   │
│                     │ Lentigo (flat pigmented macule)  │
│                     │ Nevus (mole)                     │
│                     │ Café-au-lait spots (NF1)         │
│                     │ Acanthosis nigricans              │
│                     │ Melanoma (malignant)              │
└─────────────────────┴──────────────────────────────────┘

DECREASED MELANIN PIGMENTATION (Hypomelanosis/Hypopigmentation)

┌────────────────────────────────────────────────────────┐
│          HYPOPIGMENTATION - CAUSES                     │
├─────────────────────┬──────────────────────────────────┤
│ Generalized         │ Albinism - No tyrosinase         │
│                     │ (melanocytes present, no melanin)│
├─────────────────────┼──────────────────────────────────┤
│ Localized           │ Vitiligo - Autoimmune destruction │
│                     │ of melanocytes                   │
│                     │ Pityriasis versicolor (fungal)   │
│                     │ Leprosy (anesthetic patches)     │
│                     │ Post-inflammatory                │
└─────────────────────┴──────────────────────────────────┘

Exam Tip - Albinism vs Vitiligo:

• Albinism: Melanocytes PRESENT, enzyme (tyrosinase) ABSENT
• Vitiligo: Melanocytes ABSENT (autoimmune destruction)

TOPIC 2B: CLASSIFICATION OF AMYLOIDOSIS

Definition

Properties of Amyloid

• Amorphous, eosinophilic, hyaline material on H&E
• Congo red stain → apple-green birefringence under polarized light ← PATHOGNOMONIC
• Crystal violet / Methyl violet → metachromasia
• PAS positive
• Electron microscopy: rigid non-branching fibrils (7.5-10 nm diameter)

Classification of Amyloidosis (Robbins / Harsh Mohan)

┌────────────────────────────────────────────────────────────────────┐
│                   CLASSIFICATION OF AMYLOIDOSIS                    │
├──────────────────┬──────────────┬──────────────────────────────────┤
│ TYPE             │ PROTEIN (AA) │ ASSOCIATED CONDITIONS            │
├──────────────────┼──────────────┼──────────────────────────────────┤
│ PRIMARY          │ AL (Light    │ Multiple myeloma,                │
│ (Plasma cell     │ chain)       │ Monoclonal gammopathy (no myeloma)│
│ dyscrasia)       │              │ Most COMMON form overall         │
├──────────────────┼──────────────┼──────────────────────────────────┤
│ SECONDARY        │ AA (Serum    │ TB, Osteomyelitis, Bronchiectasis,│
│ (Reactive        │ Amyloid A    │ Leprosy, RA, SLE, IBD,          │
│ systemic)        │ protein)     │ Hodgkin's lymphoma               │
├──────────────────┼──────────────┼──────────────────────────────────┤
│ HEREDITARY/      │ Transthyretin│ Familial Mediterranean fever     │
│ FAMILIAL         │ (TTR),       │ (AA), Familial polyneuropathy    │
│                  │ variants     │ (ATTR), Familial cardiomyopathy  │
├──────────────────┼──────────────┼──────────────────────────────────┤
│ SENILE SYSTEMIC  │ TTR (wild    │ Old age; mainly heart, vessels   │
│                  │ type)        │                                  │
├──────────────────┼──────────────┼──────────────────────────────────┤
│ DIALYSIS-        │ Beta-2       │ Long-term hemodialysis           │
│ ASSOCIATED       │ microglobulin│ Carpal tunnel syndrome           │
├──────────────────┼──────────────┼──────────────────────────────────┤
│ LOCALIZED        │ Various      │ Alzheimer's (Abeta/APP),         │
│                  │              │ Type 2 DM (IAPP/amylin),        │
│                  │              │ Medullary thyroid carcinoma      │
└──────────────────┴──────────────┴──────────────────────────────────┘

Organs Involved & Gross/Histology

GROSS (in secondary/systemic):
- Kidney: Large, pale, waxy, firm ("lardaceous kidney")
- Spleen: 
  → "Sago spleen" = amyloid in follicles (white specks)
  → "Lardaceous spleen" = amyloid in sinusoids (uniform large)
- Liver: Enlarged, pale, waxy appearance
- Heart: Firm, rubbery, "boiled meat" appearance

HISTOLOGY:
- H&E: Amorphous, homogeneous, eosinophilic deposits
- Congo red: Apple-green birefringence (DIAGNOSTIC) ←★
- EM: 7.5-10 nm rigid non-branching fibrils

TOPIC 3: ACUTE vs CHRONIC INFLAMMATION - DIFFERENCES

┌─────────────────────┬───────────────────────┬──────────────────────┐
│ FEATURE             │ ACUTE INFLAMMATION    │ CHRONIC INFLAMMATION │
├─────────────────────┼───────────────────────┼──────────────────────┤
│ Onset               │ Rapid (hours-days)    │ Slow (weeks-months)  │
│ Duration            │ Days to weeks         │ Weeks to years       │
│ Predominant cells   │ Neutrophils           │ Lymphocytes,         │
│                     │                       │ Macrophages,         │
│                     │                       │ Plasma cells,        │
│                     │                       │ Eosinophils          │
│ Vascular changes    │ Vasodilation,         │ Neovascularization   │
│                     │ increased permeability│ (angiogenesis)       │
│ Exudate             │ Serous/fibrinous/     │ Minimal exudate      │
│                     │ purulent              │                      │
│ Edema               │ Prominent             │ Less prominent       │
│ Tissue destruction  │ Mild                  │ Prominent (ongoing)  │
│ Fibrosis            │ Absent                │ Present              │
│ Healing             │ Resolution /          │ Scarring / fibrosis  │
│                     │ regeneration possible │                      │
│ Granuloma           │ Absent                │ Present (in some)    │
│ Mediators           │ Histamine, PGs,       │ Cytokines (IFN-γ,    │
│                     │ Leukotrienes,         │ TNF, IL-1, IL-6),   │
│                     │ Complement,           │ Growth factors       │
│                     │ Kinins                │ (TGF-β, FGF)        │
│ Example causes      │ Bacterial infection,  │ TB, sarcoidosis,     │
│                     │ trauma, burn, allergy │ autoimmune, viral,   │
│                     │                       │ foreign body         │
│ Macroscopic         │ Redness, swelling,    │ May be subtle; mass  │
│ features            │ heat, pain, loss of  │ lesion, sinus, fistula│
│                     │ function              │                      │
└─────────────────────┴───────────────────────┴──────────────────────┘

Cardinal Signs of Acute Inflammation (Celsus + Virchow)

1. Rubor (Redness) - vasodilation
2. Tumor (Swelling) - edema
3. Calor (Heat) - vasodilation
4. Dolor (Pain) - bradykinin, PGE2
5. Functio laesa (Loss of function) - added by Virchow

Types of Chronic Inflammation

1. Non-specific - diffuse infiltrate (e.g., chronic tonsillitis)
2. Granulomatous - discrete granulomas (TB, sarcoidosis, leprosy, syphilis, Crohn's)

Granuloma Structure (Exam Must-Know)

┌────────────────────────────────────────────────────────┐
│              STRUCTURE OF A GRANULOMA                  │
│                                                        │
│  Central caseous necrosis (in TB) / No necrosis       │
│  (in sarcoidosis)                                      │
│       ↓                                               │
│  Epithelioid cells (activated macrophages)             │
│       ↓                                               │
│  Langhans giant cells (nuclei at periphery)            │
│  (peripherally arranged nuclei in horseshoe pattern)  │
│       ↓                                               │
│  Surrounding rim of lymphocytes                        │
│       ↓                                               │
│  Outer fibrous collar                                  │
└────────────────────────────────────────────────────────┘

TOPIC 4: PULMONARY TUBERCULOSIS - MORPHOLOGICAL FEATURES

Types of Pulmonary TB

PRIMARY TB                          POST-PRIMARY (SECONDARY) TB
(1st infection, non-immune)         (Re-infection or reactivation)
└── Ghon's focus                    └── Simon foci → Fibrocaseous TB
    (Subpleural, upper lower lobe)
    + Hilar lymph nodes
    = Ghon's complex

Morphological Lesions

Basic Lesion = TUBERCLE (Granuloma)

TUBERCLE STRUCTURE:
┌─────────────────────────────────────────────────┐
│  3 zones (from center to periphery):            │
│                                                 │
│  1. Central CASEOUS NECROSIS                   │
│     (cheese-like, pale yellow, acellular)       │
│     (Pathognomonic of TB)                       │
│                                                 │
│  2. Epithelioid cells + Langhans Giant Cells    │
│     (Langhans = nuclei at periphery of cell,    │
│     horseshoe/arc arrangement)                  │
│                                                 │
│  3. Lymphocytes, fibroblasts, plasma cells      │
└─────────────────────────────────────────────────┘

GROSS MORPHOLOGY SEQUENCE:

Solid tubercle → Caseation → Liquefaction → Cavity → Healing

1. MILIARY TUBERCLES
   - Multiple 1-2 mm yellow-white nodules
   - Scattered throughout lung (millet seed)
   - In primary/disseminated TB

2. FIBROCASEOUS TB (most common form of secondary TB)
   - Gross: Yellowish caseous areas + fibrosis + calcification
   - Apical + posterior segments of upper lobe (↑O2 tension)
   - Healed = fibrosis/calcification
   - Active = cavitation

3. TUBERCULAR CAVITY
   - Caseous material liquefies → expelled via bronchus
   - Gross: Cavity with thick fibrous wall
   - Inner layer: caseous material / necrotic
   - Middle: Granulation tissue
   - Outer: Fibrous wall
   - May contain Rasmussen's aneurysm (erosion of branch of pulmonary artery)

4. GHON'S FOCUS (Primary)
   - 1-2 cm area of caseation; subpleural
   - Lower part of upper lobe / upper part of lower lobe
   - + Hilar lymph node caseation = Ghon's Complex

5. SIMON FOCI
   - Small calcified foci at lung apex
   - From hematogenous seeding in primary TB
   - Source for secondary TB reactivation

6. LOBAR/CASEOUS PNEUMONIA
   - Entire lobe replaced by caseous consolidation
   - Rare, severe, immunocompromised

Histopathology (Easy-to-Draw Diagram):

H&E Section of Tuberculous Granuloma:

      [Lymphocytes]
         |
    ----ring----
   |            |
[Epithelioid] [Epithelioid]
  cells          cells
   |              |
  [Langhans]    [Epithelioid]
  Giant cell
  (horseshoe 
   nuclei)
         |
    [CASEOUS NECROSIS]
    (pink, granular, 
     acellular center)
         |
    [Fibroblasts at periphery]

Staining:

• H&E: Granuloma with caseous necrosis
• ZN stain (Ziehl-Neelsen): Red bacilli on blue background (AFB)
• Wade-Fite stain: For leprosy
• PAS: Fungal infections

TOPIC 5: PARANEOPLASTIC SYNDROMES

Definition

• Direct local invasion
• Metastasis
• Elaboration of hormones native to the tissue of origin

Importance (4 Reasons):

1. May be earliest manifestation of occult malignancy
2. Cause significant morbidity, may be lethal
3. May mimic metastasis → confound treatment
4. Monitor treatment response

Classification of Paraneoplastic Syndromes:

┌──────────────────────────────────────────────────────────────────────┐
│              PARANEOPLASTIC SYNDROMES - CLASSIFICATION               │
├──────────────┬────────────────────────────────┬─────────────────────┤
│ CATEGORY     │ SYNDROME                       │ TUMOUR              │
├──────────────┼────────────────────────────────┼─────────────────────┤
│              │ Cushing syndrome               │ Small cell Ca lung, │
│              │ (↑ACTH)                        │ pancreatic Ca        │
│              ├────────────────────────────────┼─────────────────────┤
│              │ SIADH                          │ Small cell Ca lung  │
│ ENDOCRINE    │ (inappropriate ADH)            │                     │
│              ├────────────────────────────────┼─────────────────────┤
│              │ Hypercalcemia                  │ Sq cell Ca lung,    │
│              │ (PTHrP, TGF-α, TNF, IL-1)     │ Breast Ca, Renal Ca │
│              ├────────────────────────────────┼─────────────────────┤
│              │ Hypoglycemia                   │ Insulinoma,         │
│              │ (insulin-like substance)       │ Fibrosarcoma        │
│              ├────────────────────────────────┼─────────────────────┤
│              │ Polycythemia (erythropoietin)  │ Renal Ca, HCC       │
├──────────────┼────────────────────────────────┼─────────────────────┤
│ NEURO-       │ Myasthenic syndrome            │ Bronchogenic Ca,    │
│ MUSCULAR     │ (Eaton-Lambert)                │ Thymoma             │
│              │ Peripheral neuropathy          │ Breast Ca           │
│              │ Cerebellar degeneration        │ Various             │
├──────────────┼────────────────────────────────┼─────────────────────┤
│ DERMATO-     │ Acanthosis nigricans            │ Gastric, Lung,      │
│ LOGICAL      │ Dermatomyositis                │ Uterine Ca          │
├──────────────┼────────────────────────────────┼─────────────────────┤
│ OSSEOUS/     │ Hypertrophic osteoarthropathy  │ Bronchogenic Ca     │
│ ARTICULAR    │ + Clubbing of fingers          │                     │
├──────────────┼────────────────────────────────┼─────────────────────┤
│ HEMATOLOGIC  │ Venous thrombosis              │ Pancreatic Ca,      │
│              │ (Trousseau's sign)             │ Bronchogenic Ca     │
│              │ DIC                            │ AML (M3), Prostate  │
│              │ Non-bacterial thrombotic       │ Advanced cancers    │
│              │ endocarditis (NBTE)            │                     │
└──────────────┴────────────────────────────────┴─────────────────────┘

★ Most common paraneoplastic endocrinopathy: Hypercalcemia ★ Most common tumor causing paraneoplastic syndromes: Small cell carcinoma of lung

TOPIC 6: UTILITY OF FROZEN SECTIONS

Definition

Utility / Indications:

┌─────────────────────────────────────────────────────────────┐
│            UTILITY OF FROZEN SECTIONS                       │
├────┬────────────────────────────────────────────────────────┤
│ 1  │ INTRAOPERATIVE DIAGNOSIS                               │
│    │ - Determine if a lesion is benign or malignant         │
│    │ - Guide extent of surgery (conservative vs radical)    │
│    │   → Breast lump: determine if Ca → proceed to          │
│    │     mastectomy or stop at lumpectomy                   │
│    │                                                        │
│ 2  │ STATUS OF SURGICAL MARGINS                             │
│    │ - Check if tumor-free margins achieved                 │
│    │ - If margins positive → surgeon excises more           │
│    │ - Critical in head/neck, breast, skin surgeries        │
│    │                                                        │
│ 3  │ ASSESSMENT OF LYMPH NODES                              │
│    │ - Sentinel lymph node biopsy                           │
│    │ - Check for metastasis → guides lymph node dissection  │
│    │                                                        │
│ 4  │ TISSUE IDENTIFICATION                                  │
│    │ - Confirm adequate tissue has been sampled             │
│    │ - Differentiate tumor from normal tissue               │
│    │ - Identify parathyroid tissue during neck surgery      │
│    │                                                        │
│ 5  │ DEMONSTRATE LIPIDS & LIPID-CONTAINING LESIONS          │
│    │ - Oil Red O / Sudan IV stains on frozen sections       │
│    │ (Lipid dissolves in routine paraffin processing)       │
│    │                                                        │
│ 6  │ DEMONSTRATE CERTAIN ENZYMES                            │
│    │ - Enzyme histochemistry (activity lost in fixation)    │
│    │ - ATPase, NADH-TR (in muscle biopsies for myopathies) │
│    │                                                        │
│ 7  │ IMMUNOFLUORESCENCE                                     │
│    │ - Kidney biopsy (IgG, IgA, IgM, C3 deposits)          │
│    │ - Skin biopsy (DIF for pemphigus, SLE)                 │
│    │ (Some antibodies only work on frozen unfixed tissue)   │
└────┴────────────────────────────────────────────────────────┘

Disadvantages of Frozen Sections:

1. Poor morphological detail (compared to paraffin sections)
2. Cannot do all special stains
3. Requires skilled pathologist (rapid reading)
4. Not suitable for: calcified tissue, bone, very fatty tissue
5. False positive/negative possible if sampling error

Time Comparison:

Frozen Section: 15-20 minutes (intraoperative)
Paraffin Section: 24-48 hours (routine)

TOPIC 7: NEOPLASIA - DEFINITION AND ETIOPATHOGENESIS

Definition (Willis, 1952 - Classic):

"A neoplasm is an abnormal mass of tissue, the growth of which exceeds and is uncoordinated with that of normal tissues, and persists in the same excessive manner after cessation of the stimuli which evoked the change."

• Simple: Abnormal, uncontrolled, purposeless, progressive, autonomous proliferation of cells

Classification of Neoplasms:

┌──────────────────────────────────────────────────────┐
│              CLASSIFICATION OF NEOPLASMS             │
├──────────────────────┬───────────────────────────────┤
│ BENIGN               │ MALIGNANT                     │
├──────────────────────┼───────────────────────────────┤
│ Well differentiated  │ Poorly differentiated         │
│ Slow growth          │ Rapid growth                  │
│ Encapsulated         │ Invasive, non-encapsulated     │
│ No metastasis        │ Metastasis common              │
│ No recurrence        │ Recurrence likely              │
│ Normal mitoses       │ Abnormal/atypical mitoses      │
│ (if any)             │                               │
│ No necrosis          │ Necrosis and hemorrhage        │
│ Low N:C ratio        │ High N:C ratio                │
├──────────────────────┴───────────────────────────────┤
│         NAMING CONVENTION                            │
├──────────────────────┬───────────────────────────────┤
│ Tissue of Origin     │ Benign       │ Malignant       │
├──────────────────────┼──────────────┼─────────────────┤
│ Epithelium           │ Papilloma/   │ Carcinoma       │
│ (squamous/glandular) │ Adenoma      │ (SCC/AdCa)      │
│ Fibrous tissue       │ Fibroma      │ Fibrosarcoma    │
│ Cartilage            │ Chondroma    │ Chondrosarcoma  │
│ Bone                 │ Osteoma      │ Osteosarcoma    │
│ Fat                  │ Lipoma       │ Liposarcoma     │
│ Blood vessels        │ Hemangioma   │ Angiosarcoma    │
│ Smooth muscle        │ Leiomyoma    │ Leiomyosarcoma  │
│ Melanocytes          │ Nevus        │ Melanoma        │
└──────────────────────┴──────────────┴─────────────────┘

Etiopathogenesis of Neoplasms

Fundamental Principle:

Neoplasia results from accumulated mutations in proto-oncogenes and tumor suppressor genes within somatic cells (or germline), leading to clonal expansion of abnormal cells.

Two-Step Model of Carcinogenesis:

NORMAL CELL → INITIATION → PROMOTION → PROGRESSION → CANCER

1. INITIATION: Irreversible DNA mutation (carcinogen)
2. PROMOTION: Clonal expansion of initiated cells (reversible)
3. PROGRESSION: Additional mutations → malignant phenotype

Molecular Basis - 4 Key Gene Categories:

┌────────────────────────────────────────────────────────────────┐
│         GENETIC BASIS OF NEOPLASIA                            │
├──────────────────┬─────────────────────────────────────────────┤
│ 1. PROTO-        │ Normal genes → Regulate cell growth         │
│ ONCOGENES        │ Mutation → ONCOGENES → gain of function     │
│ (Accelerator)    │ Act as DOMINANT (one allele enough)         │
│                  │ Examples:                                    │
│                  │ • RAS (point mutation) - most common        │
│                  │ • MYC (amplification) - Burkitt's lymphoma  │
│                  │ • HER2/neu - breast cancer                  │
│                  │ • BCR-ABL (translocation) - CML             │
│                  │ • RET - papillary thyroid Ca                │
├──────────────────┼─────────────────────────────────────────────┤
│ 2. TUMOR         │ Normally INHIBIT cell growth (brakes)       │
│ SUPPRESSOR       │ Both alleles must be inactivated            │
│ GENES (Brakes)   │ (Knudson's "Two-Hit Hypothesis")            │
│                  │ Examples:                                    │
│                  │ • RB (retinoblastoma) - G1/S checkpoint     │
│                  │ • TP53 ("Guardian of the genome") - most    │
│                  │   commonly mutated gene in cancers          │
│                  │ • APC - colorectal cancer                   │
│                  │ • BRCA1/2 - breast, ovarian Ca              │
│                  │ • PTEN - endometrial, prostate              │
│                  │ • VHL - renal cell carcinoma                │
├──────────────────┼─────────────────────────────────────────────┤
│ 3. APOPTOSIS-    │ BCL-2 overexpression → inhibits apoptosis   │
│ REGULATING       │ → cells accumulate (Follicular lymphoma)    │
│ GENES            │ Loss of p53 → no apoptosis after DNA damage │
├──────────────────┼─────────────────────────────────────────────┤
│ 4. DNA REPAIR    │ Defects → accumulate mutations faster       │
│ GENES            │ Lynch syndrome (HNPCC) - MMR genes          │
│ (Caretakers)     │ Xeroderma pigmentosum - nucleotide excision │
│                  │ BRCA1/2 - double-strand break repair        │
└──────────────────┴─────────────────────────────────────────────┘

Hallmarks of Cancer (Hanahan & Weinberg):

┌──────────────────────────────────────────────────┐
│           8 HALLMARKS OF CANCER                  │
│                                                  │
│  1. Self-sufficiency in growth signals           │
│     (oncogenes, growth factor receptors)         │
│                                                  │
│  2. Insensitivity to anti-growth signals         │
│     (RB, TGF-β pathway loss)                     │
│                                                  │
│  3. Evasion of apoptosis                         │
│     (BCL-2↑, TP53 loss)                          │
│                                                  │
│  4. Limitless replicative potential              │
│     (Telomerase reactivation)                    │
│                                                  │
│  5. Sustained angiogenesis                       │
│     (VEGF↑)                                      │
│                                                  │
│  6. Tissue invasion and metastasis               │
│     (E-cadherin loss, MMP↑)                      │
│                                                  │
│  7. Reprogramming energy metabolism              │
│     (Warburg effect - aerobic glycolysis)        │
│                                                  │
│  8. Evading immune destruction                  │
│     (PD-L1↑, reduced MHC-I)                     │
└──────────────────────────────────────────────────┘

Carcinogenic Agents:

┌───────────────────────────────────────────────────────────────────┐
│                    ETIOLOGY OF CANCER                            │
├─────────────────────┬─────────────────────────────────────────────┤
│ A. CHEMICAL         │ Direct-acting: Alkylating agents            │
│ CARCINOGENS         │ Indirect (Procarcinogens):                  │
│                     │ • Polycyclic aromatic hydrocarbons (PAH)    │
│                     │   (tobacco smoke, coal tar)                 │
│                     │ • Aromatic amines (bladder Ca - naphthylamine)│
│                     │ • Azo dyes                                  │
│                     │ • Nitrosamines (gastric Ca)                 │
│                     │ • Aflatoxin B1 (hepatocellular Ca)          │
│                     │ • Asbestos (mesothelioma, lung Ca)          │
│                     │ • Benzene (leukemia)                        │
│                     │ • Vinyl chloride (angiosarcoma liver)       │
├─────────────────────┼─────────────────────────────────────────────┤
│ B. RADIATION        │ Ionizing: X-rays, gamma rays, nuclear       │
│ CARCINOGENS         │ → leukemia, thyroid Ca, skin Ca             │
│                     │ UV radiation: skin Ca (squamous,basal,      │
│                     │ melanoma) - via CPD, 6-4 PP in DNA          │
│                     │ (p53 mutations "sunlight signature")        │
├─────────────────────┼─────────────────────────────────────────────┤
│ C. ONCOGENIC        │ RNA viruses:                                │
│ VIRUSES             │ • HTLV-1 → Adult T-cell leukemia/lymphoma   │
│                     │ DNA viruses:                                │
│                     │ • HPV 16, 18 → Cervical Ca (E6→p53,        │
│                     │   E7→Rb inactivation)                       │
│                     │ • EBV → Burkitt's lymphoma, NPC,            │
│                     │   Hodgkin lymphoma                          │
│                     │ • HBV/HCV → Hepatocellular Ca               │
│                     │ • KSHV/HHV-8 → Kaposi sarcoma              │
│ H. PYLORI           │ Gastric MALT lymphoma, gastric Ca           │
├─────────────────────┼─────────────────────────────────────────────┤
│ D. HEREDITARY       │ Autosomal dominant (TSG loss):              │
│ FACTORS             │ • Retinoblastoma (RB1)                      │
│                     │ • Li-Fraumeni syndrome (TP53)               │
│                     │ • FAP/HNPCC (colorectal)                    │
│                     │ • BRCA1/2 (breast/ovary)                    │
│                     │ • NF1, NF2                                  │
│                     │ • VHL (renal)                               │
├─────────────────────┼─────────────────────────────────────────────┤
│ E. HOST FACTORS     │ Age, sex, obesity, immunosuppression,       │
│                     │ chronic inflammation (Barrett's → AdCa,     │
│                     │ UC → colorectal Ca, cirrhosis → HCC)        │
└─────────────────────┴─────────────────────────────────────────────┘

Mechanism of Carcinogenesis (Summary Flowchart):

INITIATING AGENT
(Chemical / Radiation / Virus)
         |
         ↓
DNA DAMAGE / MUTATION
         |
    ┌────┴────┐
    │         │
PROTO-ONCOGENE   TUMOR SUPPRESSOR
ACTIVATION      GENE INACTIVATION
(RAS, MYC, etc)  (p53, RB, APC)
    │         │
    └────┬────┘
         ↓
DISRUPTED CELL CYCLE CONTROL
+ IMPAIRED APOPTOSIS
+ DNA REPAIR DEFECTS
         ↓
CLONAL EXPANSION
         ↓
ACCUMULATION OF MORE MUTATIONS
(PROGRESSION)
         ↓
INVASION → ANGIOGENESIS → METASTASIS

QUICK EXAM REFERENCE CARD

Sources: Robbins & Kumar Basic Pathology (9780323790185); Robbins, Cotran & Kumar Pathologic Basis of Disease (9780443264528); Harsh Mohan Textbook of Pathology framework for 2nd MBBS MUHS.