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NEOPLASIA - Robbins Pathology Notes

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1. DEFINITIONS

• Neoplasia = "new growth"; neoplastic cells replicate incessantly due to resistance to normal regulatory influences
• Tumor / Neoplasm = abnormal mass of tissue whose growth exceeds and is uncoordinated with that of normal tissue and persists after the stimulus ceases
• Oncology = study of tumors (from Greek oncos)
• All neoplasms have two basic components:
  • Parenchyma - the neoplastic/transformed cells; determines biologic behavior and naming
  • Stroma - host-derived supporting connective tissue, inflammatory cells, and blood vessels; provides blood supply; essential for tumor growth; carries on two-way conversation with tumor cells

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2. NOMENCLATURE

Benign Tumors

Malignant Tumors

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3. CHARACTERISTICS OF BENIGN VS. MALIGNANT NEOPLASMS

3.1 Differentiation and Anaplasia

• Pleomorphism (variation in cell and nuclear size/shape)
• Abnormal nuclear morphology (hyperchromatic, coarse chromatin, prominent nucleoli)
• Atypical mitoses (abnormal spindle formation)
• Loss of polarity
• Tumor giant cells
• Areas of ischemic necrosis (rapid growth outstrips blood supply)

3.2 Local Invasion

• Benign tumors grow as cohesive expansile masses, develop a fibrous capsule, and remain localized. They do NOT invade surrounding tissue.
• Malignant tumors invade adjacent tissues. They lack a well-formed capsule. Some may appear encapsulated but microscopy reveals invasion. Even a thin rim of fibrous tissue does not guarantee benignancy.

3.3 Metastasis

• Benign tumors do NOT metastasize.
• Malignant tumors have the capacity to metastasize; this is the single most important feature distinguishing benign from malignant.
• ~30% of newly diagnosed cancer patients have clinically detectable metastases; another 20% have occult metastases at the time of diagnosis.

1. Seeding of body cavities - e.g., ovarian carcinoma spreading through the peritoneal cavity, mesothelioma seeding the pleural space
2. Lymphatic spread - most common for carcinomas; follows natural lymphatic drainage. Sentinel lymph node = first node to receive lymph drainage from the primary tumor; biopsy used to stage cancer
3. Hematogenous spread - more common for sarcomas; veins are penetrated more easily than arteries. Portal drainage → liver; systemic venous drainage → lungs; vertebral plexus → vertebral column

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4. EPIDEMIOLOGY

• Worldwide (2018): >17 million cancer cases; 9.6 million deaths (~26,300/day)
• US (2022 estimate): 1.9 million new cases; 609,000 deaths
• Death rates have decreased ~20% in men and ~10% in women since 1995
• In men: decreased lung, prostate, colon cancer deaths (80% of decrease)
• In women: decreased breast and colorectal cancer deaths (60% of decrease)

Environmental Factors

• Dominant risk factors for many common cancers
• Geographic variation in cancer rates reflects different environmental exposures
• Key factors: tobacco (most important), diet, alcohol, obesity, infectious agents, radiation, chemical carcinogens

Age

• Cancer risk increases with age, mostly due to accumulation of somatic mutations
• Some cancers occur predominantly in children (e.g., ALL, nephroblastoma/Wilms tumor, retinoblastoma, neuroblastoma)

Acquired Predisposing Conditions

1. Chronic inflammation - increases cancer risk (e.g., H. pylori → gastric cancer; hepatitis B/C → hepatocellular carcinoma; Barrett esophagus → esophageal adenocarcinoma; inflammatory bowel disease → colorectal carcinoma)
2. Precancerous conditions (increased risk but not inevitable):
   • Chronic atrophic gastritis
   • Solar keratosis of the skin
   • Ulcerative colitis
   • Leukoplakia of oral cavity/vulva/penis
   • Villous adenomas of the colon
3. Excessive hormonal stimulation - e.g., unopposed estrogen → endometrial carcinoma

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5. GENETIC LESIONS IN CANCER

5.1 Driver vs. Passenger Mutations

• Driver mutations - provide growth advantage; directly contribute to cancer development
• Passenger mutations - "neutral" hitchhiker mutations that don't provide growth advantage
• Important: passenger mutations can become driver mutations if selective pressure changes (e.g., during drug treatment)

5.2 Types of Genetic Lesions

5.3 MicroRNAs (miRNAs) and Cancer

• miRNAs are small non-coding RNAs that regulate gene expression post-transcriptionally
• Overexpression of miRNA → reduced expression of tumor suppressor genes
• Loss of miRNA expression → overexpression of oncogenes
• miR-21 is overexpressed in many tumors; miR-15a/miR-16-1 are deleted in many CLL cases

5.4 Epigenetic Modifications

• DNA methylation of CpG islands in promoters → gene silencing
• Histone modifications alter chromatin structure
• Tumor suppressor genes may be silenced by epigenetic changes (even without mutation)
• Implication: epigenetic silencing is potentially reversible - therapeutic target

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6. CARCINOGENESIS: A MULTISTEP PROCESS

• Cancer arises from the progressive accumulation of mutations in multiple genes
• Tumors evolve through clonal expansion with each successive mutation providing growth advantage
• Two key concepts:
  • Initiation - initial DNA damage creating a mutated cell
  • Promotion - subsequent stimulation of initiated cells to proliferate

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7. HALLMARKS OF CANCER

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7.1 Self-Sufficiency in Growth Signals

• Tumor cells secrete their own growth factors (e.g., PDGF in brain tumors, TGF-α in some carcinomas)
• Creates autocrine loop

• Mutations cause constitutive receptor activity (no ligand needed)
• HER2 (ERBB2) - amplified/overexpressed in 20-25% of breast cancers → constitutively active tyrosine kinase → targeted by trastuzumab (Herceptin)
• EGFR (HER1) - overexpressed in lung and other carcinomas
• FLT3 - mutated in acute myeloid leukemia

• RAS - most commonly mutated oncogene in human cancers (~30% of all cancers)
  • RAS is a GTP-binding protein; active when GTP-bound, inactive when GDP-bound
  • Mutations (codons 12, 13, 61) impair GTPase activity → permanently GTP-bound → constitutively active
  • Activates downstream: RAF/MAPK pathway and PI3K/AKT pathway
• BCR-ABL (CML) - translocation t(9;22) creates Philadelphia chromosome; BCR-ABL fusion protein has constitutively active tyrosine kinase activity → targeted by imatinib (Gleevec)
• BRAF - mutated in ~60% of melanomas; targeted by vemurafenib

• MYC - regulates expression of many growth-promoting genes; overexpressed or amplified in many cancers (Burkitt lymphoma: t(8;14) MYC translocation)
• MYCN - amplified in neuroblastoma

• Cell cycle progression controlled by cyclin-CDK complexes
• CDK inhibitors (CDKIs) normally brake cell cycle at G1/S and G2/M checkpoints
• Cyclin D - overexpressed in breast, esophageal, and other cancers → drives cells past G1/S checkpoint
• CDK4 - amplified in some sarcomas

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7.2 Insensitivity to Growth Inhibitory Signals: Tumor Suppressor Genes

• Location: 13q14
• Protein: pRB - critical regulator of G1/S transition
• Mechanism: Hypophosphorylated pRB binds and sequesters E2F transcription factors; when phosphorylated by cyclin D-CDK4/6 complex → releases E2F → cell enters S phase
• In cancer: Loss of RB means E2F is always free → uncontrolled S phase entry
• Clinical associations:
  • Retinoblastoma: inherited (germline 1 hit + somatic 1 hit) or sporadic (2 somatic hits)
  • Also lost in osteosarcoma, breast, lung, bladder cancers

• Most commonly mutated gene in human cancers (majority of cancers)
• Location: 17p13
• Protein: p53 - transcription factor activated by cellular stress

1. Cell cycle arrest at G1 (via p21 induction → CDK inhibition → RB stays active)
2. DNA damage repair gene induction
3. Senescence induction (permanent G1 arrest with specific chromatin changes)
4. Apoptosis (via upregulation of proapoptotic genes e.g., BAX)

• In normal cells: p53 levels low due to MDM2 ubiquitin-mediated degradation
• On DNA damage: kinases phosphorylate p53 → cannot be degraded by MDM2 → p53 accumulates
• After successful repair: p53 upregulates MDM2 → destroys itself → cell cycle resumes
• Li-Fraumeni syndrome: germline TP53 mutation → multiple early-onset cancers

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7.3 Altered Cellular Metabolism (Warburg Effect)

• Normal cells: aerobic respiration (oxidative phosphorylation)
• Cancer cells: predominantly use aerobic glycolysis (glycolysis even in the presence of O2) - the Warburg effect
• Glycolysis produces less ATP per glucose but:
  • Provides rapid energy
  • Generates biosynthetic intermediates for building new cells
  • Reduces oxidative damage
• Clinical application: Basis for FDG-PET scanning (cancer cells take up more 18F-FDG due to upregulated glucose transporters)
• Oncometabolism: IDH1/IDH2 mutations (found in gliomas, AML) produce 2-hydroxyglutarate, an oncometabolite that drives epigenetic changes
• Autophagy: Cancer cells may exploit autophagy to survive nutrient deprivation; complex dual role (suppressive early, supportive later)

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7.4 Evasion of Apoptosis

• Intrinsic (mitochondrial) pathway: Regulated by BCL2 family (proapoptotic: BAX, BAK; antiapoptotic: BCL2, BCL-XL, MCL1)
• Extrinsic (death receptor) pathway: FAS ligand binds FAS receptor → caspase-8 activation

• BCL2 overexpression - most common; t(14;18) in follicular lymphoma brings BCL2 under Ig promoter → constitutive BCL2 expression → apoptosis resistance
• Loss of TP53 - removes apoptosis trigger
• Upregulation of survival signals (PI3K/AKT pathway)
• Loss of FAS or FAS-L receptor expression

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7.5 Limitless Replicative Potential (Immortality)

• Normal cells: limited cell divisions due to progressive telomere shortening → senescence or apoptosis ("Hayflick limit" ~60-70 divisions)
• Telomeres: TTAGGG repeats at chromosome ends; maintained by telomerase
• Normal somatic cells: telomerase inactive → telomeres shorten with each division
• Cancer cells: reactivate telomerase (TERT) → maintain telomere length → unlimited replication
• Telomerase expression found in ~90% of human cancers
• HPV E6 protein stimulates TERT expression

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7.6 Sustained Angiogenesis

• Tumors >1-2mm need a blood supply; can't rely on diffusion
• Normal angiogenesis is tightly regulated by pro- and anti-angiogenic signals
• Cancer: tips the balance toward angiogenesis

• VEGF (Vascular Endothelial Growth Factor) - main driver of tumor angiogenesis; induced by hypoxia (HIF-1α pathway), RAS activation, loss of p53
• bFGF (Basic Fibroblast Growth Factor)
• Angiopoietins - stabilize/destabilize vessels

• Thrombospondin-1 (TSP-1) - induced by p53; lost when p53 is mutated
• Angiostatin, Endostatin

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7.7 Invasion and Metastasis

Steps of the Metastatic Cascade:

• Loosening of intercellular connections: Reduced E-cadherin expression (via mutation, SNAIL/TWIST transcription factors, or β-catenin activation) → cells detach
• Local ECM degradation: Tumor cells or recruited stromal cells secrete proteases:
  • Matrix metalloproteinases (MMPs) - especially MMP-2 and MMP-9 (gelatinases)
  • Cathepsin D, urokinase plasminogen activator
  • MMP-9 cleaves type IV collagen in basement membranes; also releases ECM-sequestered VEGF
• Altered cell-ECM attachment: Integrins change expression → tumor cells can migrate
• Locomotion: Chemotactic gradients (from degraded ECM, stroma, and inflammatory cells) guide tumor cell migration via actin cytoskeleton remodeling

• Tumor cells enter blood vessels (intravasation)
• In circulation, protected by platelets (form emboli)
• Arrest in capillary beds (size-dependent or receptor-mediated)
• Extravasation at distant site
• Most circulating tumor cells die - metastasis is an INEFFICIENT process

• Dormant micrometastases may persist for years
• Growth requires angiogenesis and immune evasion at new site
• Organ tropism: Chemokines/adhesion molecules at target organ match receptors on tumor cells

• Epithelial cancer cells downregulate E-cadherin and other epithelial markers
• Upregulate vimentin, N-cadherin, fibronectin (mesenchymal markers)
• Gain migratory/invasive phenotype
• Driven by SNAIL, TWIST, ZEB1/2 transcription factors

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7.8 Evasion of Immune Surveillance

• CD8+ cytotoxic T lymphocytes (CTLs) - main effectors; recognize tumor-associated antigens on MHC class I
• NK cells - kill cells lacking MHC class I
• Macrophages (M1 phenotype) - direct cytotoxicity
• Antibody-dependent cellular cytotoxicity (ADCC)

• Products of mutated oncogenes/tumor suppressors (neoantigens) - most immunogenic
• Overexpressed normal proteins (e.g., HER2)
• Cancer-testis antigens (MAGE, GAGE) - normally expressed only in testis
• Viral antigens (e.g., HPV E6/E7, EBV antigens)

• Downregulation of MHC class I → invisible to CTLs
• Loss of tumor antigens (antigen loss variants)
• Expression of immune checkpoint molecules:
  • PD-L1 on tumor cells binds PD-1 on T cells → T cell exhaustion/anergy
  • CTLA-4 on T cells → dampens T cell activation
• Secretion of immunosuppressive cytokines (TGF-β, IL-10)
• Recruitment of regulatory T cells (Tregs) and M2 macrophages into tumor microenvironment

• Anti-PD-1 (pembrolizumab, nivolumab): approved for melanoma, NSCLC, and many others
• Anti-PD-L1 (atezolizumab, durvalumab)
• Anti-CTLA-4 (ipilimumab): approved for melanoma
• Revolutionary breakthrough in cancer therapy

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Enabling Characteristics:

• Accelerates accumulation of driver mutations
• Caused by: defective DNA repair, impaired mitotic checkpoints, telomere crisis
• Microsatellite instability (MSI): Defective DNA mismatch repair (MLH1, MSH2, MSH6, PMS2) → Lynch syndrome; also sporadic colorectal, endometrial cancers
• Chromosomal instability (CIN): Aberrant mitotic spindle checkpoints → aneuploidy

• Inflammatory cells provide growth factors, survival factors, angiogenic factors, enzymes that promote invasion
• Chronic inflammation creates a permissive microenvironment for tumor progression

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8. CARCINOGENIC AGENTS

8.1 Chemical Carcinogens

• Alkylating agents (e.g., cyclophosphamide - therapeutic irony: used to treat cancer, can cause secondary AML)
• Acylating agents

• Polycyclic aromatic hydrocarbons (PAH) - in coal tar, tobacco smoke → lung, skin, bladder cancer
• Aromatic amines / azo dyes - β-naphthylamine → bladder cancer
• Aflatoxin B1 (from Aspergillus) - hepatocellular carcinoma; common in Africa/Asia
• Nitrosamines - gastric cancer
• Benzene - AML

1. Initiation - rapid, irreversible, subthreshold mutational damage to DNA
2. Promotion - repeated exposure to promoter agents (not carcinogenic alone) → proliferation of initiated cells
3. Progression - acquisition of additional mutations → malignant phenotype

8.2 Radiation

• Ionizing radiation: Causes DNA strand breaks, chromosomal aberrations, point mutations
  • UV radiation → skin cancer (squamous cell carcinoma, basal cell carcinoma, melanoma); causes pyrimidine dimers (CC→TT signature mutations) → impairs DNA repair (nucleotide excision repair)
  • X-rays, gamma rays → thyroid, breast, leukemia (AML > ALL; CLL NOT caused by radiation)
  • Japanese atomic bomb survivors → leukemia, thyroid, breast cancers
  • Xeroderma pigmentosum: autosomal recessive; defective NER → extreme UV sensitivity → multiple skin cancers

8.3 Oncogenic Viruses and Microbes

• E6 protein: binds and degrades p53; stimulates TERT (telomerase) → immortalization
• E7 protein: binds RB → releases E2F → cell cycle progression; inactivates p21
• High-risk HPV types have higher affinity for p53 and RB than low-risk types
• Integration into host genome → overexpression of E6/E7 + genomic instability

• HTLV-1 → Adult T-cell leukemia/lymphoma (ATL); Tax protein activates NF-κB → proliferation

• Chronic gastritis → gastric adenocarcinoma and MALT lymphoma
• Chronic inflammation drives carcinogenesis

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9. CLINICAL ASPECTS OF NEOPLASIA

9.1 Effects of Tumor on the Host

1. Local effects (compression, invasion, obstruction):
   • Small pituitary adenoma → hypopituitarism
   • Small leiomyoma near renal artery → renal ischemia, hypertension
   • Small bile duct carcinoma → fatal biliary obstruction
   • Tumors in gut lumen → intussusception, obstruction
2. Hormonal effects:
   • Pancreatic islet cell adenoma/carcinoma → hyperinsulinism
   • Adrenocortical adenoma/carcinoma → hyperaldosteronism (hypertension, hypokalemia)
   • Better differentiated tumors more likely to secrete hormones
3. Cachexia:
   • Progressive loss of body fat + lean body mass; profound weakness, anorexia, anemia
   • NOT caused by nutritional demands of the tumor
   • Mediated by cytokines: TNF (suppresses appetite, inhibits lipoprotein lipase), IL-1, IL-6, IFN-γ
   • Basal metabolic rate INCREASED (unlike starvation, where BMR decreases)
   • No effective treatment except removing the tumor

9.2 Paraneoplastic Syndromes

• Symptoms NOT explained by local/distant spread or by normal tissue hormone production
• Occur in 10-15% of cancer patients
• Important because:
  • May be first manifestation of occult cancer
  • May be clinically significant or lethal
  • May mimic metastasis (confound treatment)

9.3 Grading and Staging

• Grade 1 = well differentiated (low grade)
• Grade 2 = moderately differentiated
• Grade 3 = poorly differentiated
• Grade 4 = undifferentiated/anaplastic (high grade)
• Different systems for different tumors (Gleason for prostate, Fuhrman for RCC, etc.)
• Grading has LESS clinical importance than staging

• TNM system (most widely used):
  • T = size/extent of primary tumor (T1-T4)
  • N = regional lymph node involvement (N0-N3)
  • M = distant metastasis (M0 = none; M1 = present)
• Also expressed as clinical stages I-IV (Stage I = localized; Stage IV = distant metastasis)

9.4 Laboratory Diagnosis

• Biopsy (gold standard): incisional or excisional
• Fine needle aspiration (FNA): cytology of cells
• Frozen sections: rapid intraoperative diagnosis
• Core needle biopsy: good for solid tumors
• Exfoliative cytology: Pap smear (cervix), sputum, urine, pleural/peritoneal fluid

• Identifies cell lineage using antibodies to tissue-specific antigens
• Examples:
  • PSA → prostate cancer
  • ER/PR, HER2 → breast cancer
  • CD markers (CD20 → B-cell lymphoma; CD3 → T-cell lymphoma)
  • Cytokeratin → carcinoma; vimentin → sarcoma; S100 → melanoma, neural tumors
  • TTF-1 → lung adenocarcinoma; CK7/CK20 patterns distinguish primary sites
• Identifies hormone receptors for targeted therapy
• Identifies metastasis of unknown primary

• Immunophenotyping of leukemias and lymphomas
• Cell cycle analysis (DNA ploidy; S-phase fraction)

• PCR, FISH, next-generation sequencing (NGS)
• Detect gene rearrangements (BCR-ABL, IGH rearrangements)
• Identify driver mutations for targeted therapy (EGFR, ALK, RAS, BRAF, HER2)
• Microsatellite instability testing (for Lynch syndrome, anti-PD-1 therapy eligibility)
• FISH for amplifications (HER2, MYC, MYCN)
• Methylation-specific PCR for epigenetic silencing

• Serum proteins produced by tumor cells; used for monitoring, not diagnosis
• NOT adequate for cancer screening (low sensitivity/specificity)

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SUMMARY TABLE: Benign vs. Malignant

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