NEOPLASIA - Complete Long Answer (10 Marks)

Definition

Fundamental Features of Cancer Cells (Robbins)

• Cancer is a genetic disorder caused by DNA mutations - inherited, spontaneous (replication errors), or induced by mutagens.
• Genetic alterations are heritable - passed to daughter cells; cells with growth/survival advantage outcompete neighbors (Darwinian selection).
• Individual tumors are clonal - progeny of a single cell at initiation.
• Mutations impart cancer hallmarks - a set of properties governing the tumor's natural history and response to therapy.

I. NOMENCLATURE

Benign Tumors

• Fibroma (fibrous tissue), Lipoma (fat), Chondroma (cartilage), Osteoma (bone)
• Adenoma = benign epithelial tumor forming glands
• Papilloma = benign epithelial tumor forming finger-like projections
• Cystadenoma = hollow cystic adenoma

Malignant Tumors

• Carcinoma = malignant tumor of epithelial cells
  • Adenocarcinoma = glandular pattern
  • Squamous cell carcinoma = squamous differentiation
• Sarcoma = malignant tumor of mesenchymal/connective tissue
  • Fibrosarcoma, Liposarcoma, Osteosarcoma, Chondrosarcoma
• Mixed tumors = contain more than one cell type (e.g., Pleomorphic adenoma of salivary gland)
• Teratoma = contains tissues from all three germ layers (e.g., dermoid cyst of ovary)
• Blastomas = resemble embryonic/primitive tissue (e.g., retinoblastoma, nephroblastoma)

II. CHARACTERISTICS OF BENIGN VS. MALIGNANT NEOPLASMS

A. Differentiation and Anaplasia

• Well-differentiated tumors closely resemble normal parenchymal cells (e.g., well-differentiated thyroid adenocarcinoma may contain normal-looking follicles).
• Anaplastic (undifferentiated) tumors show no resemblance to normal cells; anaplasia ("backward formation") is a reliable indicator of malignancy.

1. Pleomorphism - variation in cell and nuclear size/shape
2. Hyperchromatism - darkly staining nuclei due to excess DNA
3. High nuclear-to-cytoplasmic (N:C) ratio (1:1 instead of normal 1:4 or 1:6)
4. Prominent nucleoli - often large ("owl-eye" nucleoli)
5. Abnormal mitoses - tripolar, quadripolar spindles
6. Tumor giant cells - mono- or multinucleated
7. Loss of polarity - disorganized architecture
8. Desmoplasia - dense fibrous stroma induced by some cancers

B. Local Invasion

• Benign tumors grow as cohesive, expansile masses that develop a rim of compressed connective tissue (fibrous capsule), pushing aside but not invading surrounding normal tissue.
• Malignant tumors are poorly demarcated from surrounding tissue. They infiltrate and destroy; even tumors appearing encapsulated (e.g., follicular carcinoma of thyroid) show microscopic tongues of tumor penetrating the capsule. A wide surgical margin of normal tissue must therefore be excised.
• Carcinoma in situ = pre-invasive stage; full-thickness epithelial atypia with intact basement membrane.

C. Metastasis

• ~30% of patients with newly diagnosed solid tumors present with clinically evident metastases.
• An additional ~20% have occult metastases at diagnosis.

1. Lymphatic spread - most common for carcinomas; follows anatomical lymphatic drainage (e.g., breast cancer to axillary nodes).
2. Hematogenous spread - preferred by sarcomas; arteries are harder to penetrate than veins. Liver and lungs are the most common sites (portal drainage and systemic venous return). Vertebral venous plexus (Batson's plexus) explains vertebral metastases from prostate/thyroid/kidney cancers.
3. Seeding within body cavities - particularly peritoneum (e.g., ovarian carcinoma forming "pseudomyxoma peritonei"), pleura, pericardium, subarachnoid space.

Note: Some malignant tumors rarely metastasize despite local invasiveness - basal cell carcinoma of skin and most primary CNS tumors.

III. EPIDEMIOLOGY OF CANCER

• Cancer is the second leading cause of death in the United States (after cardiovascular disease).
• Incidence varies by age, sex, geography, and environmental exposure.

Environmental / Occupational Carcinogens

Precursor (Pre-neoplastic) Lesions

• Squamous metaplasia and dysplasia of bronchial mucosa (smokers) - risk for lung carcinoma
• Endometrial hyperplasia/dysplasia (unopposed estrogen) - risk for endometrial carcinoma
• Leukoplakia of oral cavity, vulva, penis - may progress to squamous cell carcinoma
• Villous adenoma of colon - high risk for colorectal carcinoma (up to 50% malignant transformation)

IV. CARCINOGENESIS: A MULTISTEP PROCESS

• Point mutations (e.g., RAS mutations in many cancers)
• Gene rearrangements/translocations (e.g., BCR-ABL in CML)
• Gene deletions (e.g., RB deletion in retinoblastoma)
• Gene amplifications (e.g., HER2/NEU in breast cancer)
• Aneuploidy
• MicroRNA dysregulation
• Epigenetic modifications (altered DNA methylation, histone modification)

V. HALLMARKS OF CANCER

1. Self-Sufficiency in Growth Signals

• Cancer cells generate their own growth signals via proto-oncogene → oncogene conversion (gain-of-function mutations).
• Examples: Overexpression of RAS (most common oncogene in human cancers), MYC, HER2/NEU, EGFR.

2. Insensitivity to Growth-Inhibitory Signals (Tumor Suppressor Gene Loss)

• RB gene (retinoblastoma protein) - "Governor of the cell cycle." Loss removes the G1/S checkpoint brake; cells divide unchecked.
• TP53 gene (p53 protein) - "Guardian of the genome." Mutated in >50% of human cancers. Normally activates DNA repair, cell cycle arrest (via p21), or apoptosis in response to DNA damage. Loss leads to unrepaired mutations accumulating.

3. Altered Cellular Metabolism (Warburg Effect)

• Cancer cells preferentially use aerobic glycolysis (glucose → lactate even in oxygen-rich conditions), generating building blocks for rapid proliferation.

4. Evasion of Apoptosis

• Upregulation of anti-apoptotic proteins (e.g., BCL-2, amplified in follicular lymphoma via t(14;18)).
• Loss of pro-apoptotic signals (e.g., loss of p53).

5. Limitless Replicative Potential (Immortality)

• Normal cells have a finite number of divisions (Hayflick limit) due to telomere shortening.
• Cancer cells reactivate telomerase (TERT), maintaining telomere length and achieving immortality.

6. Sustained Angiogenesis

• Tumors cannot grow beyond 1-2 mm without a blood supply.
• Cancer cells secrete VEGF (Vascular Endothelial Growth Factor) and bFGF to induce new vessel formation (angiogenesis).
• Anti-VEGF therapy (bevacizumab) exploits this hallmark.

7. Invasion and Metastasis

• Cancer cells downregulate E-cadherin (cell adhesion), undergo Epithelial-to-Mesenchymal Transition (EMT), secrete matrix metalloproteinases (MMPs) to degrade the extracellular matrix, invade blood/lymph vessels, survive in circulation, and colonize distant organs.

8. Evasion of Immune Surveillance

• Cancer cells downregulate MHC class I (evading cytotoxic T cells), express PD-L1 (binding PD-1 on T cells to induce T-cell exhaustion), and secrete immunosuppressive cytokines (TGF-β, IL-10).
• Basis for checkpoint inhibitor immunotherapy (anti-PD-1, anti-CTLA-4).

• Genomic instability - defects in DNA repair (e.g., mismatch repair defects in Lynch syndrome)
• Cancer-promoting inflammation - chronic inflammation provides growth factors, reactive oxygen species causing mutations

VI. CLINICAL ASPECTS OF NEOPLASIA

Local Effects

• Space-occupying effects (compression of adjacent structures)
• Obstruction of ducts/passages
• Pathological fractures (bone metastases)
• Ulceration and hemorrhage

Systemic Effects (Paraneoplastic Syndromes)

• Hypercalcemia (PTHrP secretion - most common, e.g., squamous cell carcinoma of lung)
• Cushing syndrome (ectopic ACTH secretion - small cell carcinoma of lung)
• SIADH (ectopic ADH - small cell carcinoma)
• Polycythemia (ectopic EPO - renal cell carcinoma)
• Carcinoid syndrome (serotonin secretion - carcinoid tumors)
• Trousseau syndrome (migratory thrombophlebitis in mucin-secreting adenocarcinomas)
• Acanthosis nigricans (gastric carcinoma)
• Myasthenic (Lambert-Eaton) syndrome (small cell lung carcinoma)

Grading and Staging

• Grade I: Well-differentiated
• Grade II: Moderately differentiated
• Grade III: Poorly differentiated
• Grade IV: Undifferentiated/anaplastic

• TNM system: T (tumor size/local extent), N (lymph node involvement), M (distant metastasis)

Summary Table: Benign vs. Malignant Tumors