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NEOPLASIA - ROBBINS & COTRAN PATHOLOGIC BASIS OF DISEASE

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1. DEFINITIONS

• Neoplasia = "new growth"; an abnormal mass of tissue whose growth exceeds and is uncoordinated with that of normal tissues and persists in the same excessive manner after cessation of the stimuli that evoked it.
• Tumor = originally referred to swelling; now synonymous with neoplasm.
• Oncology = study of tumors (Greek onkos = tumor).

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2. NOMENCLATURE OF TUMORS

Benign Tumors

Malignant Tumors

Special Terms

• Teratoma - tumor containing elements of all three germ layers
• Hamartoma - disorganized but mature tissue indigenous to the site
• Choristoma - ectopic rest of normal tissue
• Blastoma - tumors of embryonic origin (e.g., nephroblastoma, retinoblastoma)

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3. CHARACTERISTICS OF BENIGN vs. MALIGNANT TUMORS

Anaplasia (Lack of Differentiation)

• Pleomorphism - variation in size and shape of cells and nuclei
• Abnormal nuclear morphology - hyperchromatic nuclei, high N:C ratio (1:1 instead of normal 1:4-1:6)
• Atypical mitoses - tripolar, quadripolar spindles
• Tumor giant cells
• Loss of polarity

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4. GROWTH OF TUMORS

Tumor Angiogenesis

• Tumors cannot grow beyond 1-2 mm without developing a blood supply
• Angiogenesis is induced by hypoxia and HIF-1α, which upregulates VEGF
• Tumor vasculature is abnormal - leaky, dilated, tortuous
• Anti-angiogenic therapy (e.g., bevacizumab, targeting VEGF) is a therapeutic approach

Rates of Growth

• Doubling time of tumor cells is generally longer than normal counterparts
• Net tumor growth = proliferation rate minus death rate
• Many cells in the tumor are not cycling (G0)
• Growth fraction = proportion of cells in the proliferative pool (typically 20% in human tumors)

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5. LOCAL INVASION AND METASTASIS

Local Invasion

• Malignant cells invade adjacent tissues by:
  1. Loosening of cell-to-cell contacts (downregulation of E-cadherin)
  2. Degradation of ECM (MMPs - matrix metalloproteinases)
  3. Attachment to ECM components (laminin, fibronectin)
  4. Cell migration through the degraded matrix

Metastasis

1. Lymphatic spread - most common for carcinomas; first to regional lymph nodes (sentinel node concept)
2. Hematogenous spread - typical of sarcomas; portal vein → liver; vena cava → lungs
3. Seeding of body cavities - e.g., ovarian cancer seeds peritoneum; called "transcoelomic spread"

Steps in Metastatic Cascade (EMT - Epithelial-Mesenchymal Transition)

1. Invasion of ECM
2. Vascular dissemination (intravasation)
3. Survival in circulation (evade NK cells; clumping with platelets)
4. Extravasation
5. Formation of micrometastases and colonization

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6. MOLECULAR BASIS OF CANCER - HALLMARKS OF CANCER

Core Hallmarks:

1. Self-sufficiency in growth signals - oncogene activation (RAS, MYC, EGFR)
2. Insensitivity to growth inhibitory signals - loss of tumor suppressor genes (RB, p53)
3. Evasion of apoptosis - BCL2 overexpression; p53 loss
4. Limitless replicative potential - telomerase activation
5. Sustained angiogenesis - VEGF upregulation
6. Ability to invade and metastasize - E-cadherin loss, MMPs
7. Reprogramming of cellular energetics (Warburg effect - aerobic glycolysis)
8. Evading immune destruction - PD-L1 expression, immunosuppressive TME

Enabling Characteristics:

• Genomic instability - enables accumulation of driver mutations
• Tumor-promoting inflammation

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7. ONCOGENES AND PROTO-ONCOGENES

Proto-oncogenes become oncogenes by:

1. Point mutations - e.g., RAS mutations (constitutively active GTPase); found in ~30% of all human cancers
2. Gene amplification - e.g., N-MYC in neuroblastoma, HER2/NEU in breast cancer
3. Chromosomal translocation - e.g., BCR-ABL in CML (t(9;22) Philadelphia chromosome); MYC in Burkitt lymphoma (t(8;14))

Key Oncogenes:

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8. TUMOR SUPPRESSOR GENES

The RB Pathway

• RB protein is active (hypophosphorylated) in G1 → binds E2F transcription factor → prevents S phase entry
• CDK4/cyclin D phosphorylates RB → releases E2F → allows cell cycle progression
• p16 (CDKN2A) inhibits CDK4 → maintains RB in active state
• Almost all cancers have some defect in the G1/S checkpoint via this pathway

The p53 Pathway

• p53 is activated by DNA damage, oxidative stress, hypoxia, oncogene activation
• Effects: cell cycle arrest (via p21), DNA repair, apoptosis (via BAX, PUMA)
• MDM2 is a negative regulator of p53; MDM2 is itself a transcriptional target of p53 (negative feedback loop)
• Li-Fraumeni syndrome: germline TP53 mutation; multiple tumors at young age

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9. APOPTOSIS EVASION IN CANCER

Intrinsic (Mitochondrial) Pathway

• BAX, BAK (pro-apoptotic) vs. BCL2, BCL-XL (anti-apoptotic)
• BCL2 overexpression in follicular lymphoma (t(14;18))
• Cytochrome c release → Apoptosome → Caspase 9 → Caspase 3

Extrinsic Pathway

• FAS ligand binds FAS → FADD → Caspase 8 → Caspase 3
• Cancers downregulate FAS/FADD to evade death

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10. TELOMERES AND CANCER

• Normal cells: telomeres shorten with each division → replicative senescence (Hayflick limit)
• Cancer cells: telomerase (TERT) is reactivated → maintains telomere length → immortality
• Dyskeratosis congenita: short telomeres; increased cancer risk
• Short telomeres → chromosomal instability → "bridge-fusion-breakage" cycles → gene amplification

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11. TUMOR MICROENVIRONMENT (TME)

• Tumors are not just clonal masses; they contain stroma: fibroblasts (cancer-associated fibroblasts, CAFs), immune cells, vasculature, ECM
• Tumor-associated macrophages (TAMs): M2 phenotype - promote tumor growth, angiogenesis, immunosuppression
• Myeloid-derived suppressor cells (MDSCs): suppress anti-tumor T cell responses
• Regulatory T cells (Tregs): suppress effector T cells
• PD-1/PD-L1 checkpoint: tumors upregulate PD-L1 to suppress T cells (checkpoint immunotherapy targets this)

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12. CARCINOGENESIS - MULTISTEP PROCESS

Steps:

1. Initiation - irreversible DNA mutation (genotoxic damage)
2. Promotion - enhanced proliferation of initiated cells (may be reversible)
3. Progression - further mutations → fully malignant phenotype

Chemical Carcinogenesis

Direct-Acting Carcinogens:

• Do NOT require metabolic activation
• Examples: alkylating agents (cyclophosphamide, busulfan), acylating agents
• Used in chemotherapy → secondary malignancies (treatment-related AML)

Indirect-Acting (Procarcinogens) → Ultimate Carcinogens:

• Require conversion by endogenous metabolic pathways (cytochrome P-450)
• Examples:
  • Benzo[a]pyrene (in cigarette smoke, coal tar) → diol-epoxide → DNA adducts
  • Azo dyes (e.g., 2-naphthylamine) → bladder cancer
  • Aflatoxin B1 (from Aspergillus flavus on peanuts/grains) → hepatocellular carcinoma; G→T transversion in TP53 codon 249
  • Nitrosamines → gastric cancer
  • Vinyl chloride → angiosarcoma of liver

Tumor Promoters (Non-genotoxic):

• Stimulate cell proliferation without direct DNA damage
• Enhance effects of carcinogens
• Examples: estrogen (breast cancer), phenobarbital (liver tumors), saccharin (bladder, animals), tissue repair responses
• Classic model: phorbol esters (TPA) in mouse skin painting experiments

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13. RADIATION CARCINOGENESIS

UV Radiation

• UVB (280-320 nm) is most carcinogenic; causes pyrimidine dimers (adjacent thymidine residues cross-linked)
• UVC (200-280 nm) is filtered by ozone layer
• Repaired by nucleotide excision repair (NER) pathway
• Xeroderma Pigmentosum (XP): defect in NER → extreme sun sensitivity → skin cancer (squamous cell carcinoma, basal cell carcinoma, melanoma)
• Risk: fair-skinned individuals; highest in Queensland, Australia
• Squamous cell carcinoma > basal cell carcinoma > melanoma (by frequency)

Ionizing Radiation

• Associated with: leukemia, thyroid cancer, breast cancer, lung cancer, sarcomas
• Hiroshima/Nagasaki survivors: spike in leukemia 7-10 years later; solid tumors later
• Chernobyl: thyroid cancer (radioactive iodine)
• Medical exposure (radium dial painters, uranium miners, radiologists)
• Mechanism: direct DNA strand breaks and free radical generation
• Cancers appear decades after exposure

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14. VIRAL AND MICROBIAL ONCOGENESIS

RNA Viruses (Retroviruses)

• Carry viral oncogenes (v-onc) derived from captured proto-oncogenes
• HTLV-1 → Adult T-cell leukemia/lymphoma (Caribbean, Japan)
  • Mechanism: Tax protein activates NF-κB and AP-1 → T cell proliferation
  • Does NOT carry a classical v-onc gene; acts via trans-activation

DNA Viruses

HPV (Human Papillomavirus)

• High-risk types: HPV 16 and 18 → cervical carcinoma, oropharyngeal carcinoma
• Low-risk types: HPV 6 and 11 → condyloma acuminata (genital warts)
• E6 protein: binds p53 → ubiquitin-mediated p53 degradation → loss of G1 checkpoint, loss of apoptosis, TERT activation (immortalization)
• E7 protein: binds and inactivates RB → releases E2F → uncontrolled cell cycle progression; also binds CDK inhibitors p21 and p27
• Combined E6+E7: immortalize cells; require co-factor (e.g., mutated RAS, cigarette smoke) for malignant transformation
• Mechanism of integration: HPV DNA integrates into host chromosome → E2 gene disrupted → loss of E2 repression of E6/E7 → overexpression of E6 and E7
• Risk factors for progression: cigarette smoking, coexisting infections, immunosuppression (HIV)

EBV (Epstein-Barr Virus)

• First human tumor-virus link: Burkitt lymphoma
• EBV receptor: CD21 (complement receptor) on B cells
• Mechanism - latent infection:
  • LMP1 (Latent Membrane Protein-1): acts as constitutively active CD40 receptor → activates NF-κB and JAK/STAT → B cell survival and proliferation → prevents apoptosis via BCL2
  • EBNA2: nuclear protein mimicking constitutively active Notch receptor → upregulates cyclin D and SRC family proto-oncogenes
  • EBV inhibits antigen presentation → blunts immune response
• In immunocompetent hosts: polyclonal B-cell proliferation controlled by cytotoxic T cells → infectious mononucleosis
• In immunocompromised (HIV, transplants): uncontrolled → EBV-associated lymphomas
• In Africa (malaria co-infection) + t(8;14) MYC translocation → Endemic Burkitt lymphoma
• Other EBV-associated cancers: Nasopharyngeal carcinoma, Hodgkin lymphoma, post-transplant lymphoproliferative disorders

HBV and HCV (Hepatitis Viruses)

• Both associated with Hepatocellular Carcinoma (HCC)
• Mechanism is multifactorial:
  • Immunologically mediated chronic inflammation
  • Hepatocellular injury → reparative proliferation → accumulation of mutations
  • HBx protein (HBV) and HCV core protein activate signal transduction pathways
  • Cirrhosis is a major predisposing condition (HCV > HBV for cirrhosis)
• HBV: DNA virus; integrates into host genome; HBx transactivates growth factor genes
• HCV: RNA virus; does NOT integrate; carcinogenesis via chronic inflammation

KSHV/HHV-8 (Kaposi Sarcoma Herpesvirus)

• Kaposi sarcoma (especially in AIDS patients)
• Primary effusion lymphoma
• Multicentric Castleman disease

Bacterial Oncogenesis

H. pylori

• Gastric adenocarcinoma (MALT lymphoma and diffuse large B-cell lymphoma too)
• Mechanism:
  • Chronic gastritis → mucosal atrophy → intestinal metaplasia → dysplasia → carcinoma
  • CagA (cytotoxin-associated gene A): virulence factor injected into gastric epithelial cells via Type IV secretion → activates growth factor pathways (SHP2, ERK)
  • Chronic B-cell stimulation → polyclonal → monoclonal → MALT lymphoma
  • Early MALT lymphomas may regress with H. pylori eradication

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15. CLINICAL ASPECTS OF NEOPLASIA

Local and Hormonal Effects

• Location is critical: 1 cm pituitary adenoma can cause hypopituitarism
• Tumors in gut → obstruction; may cause intussusception (peristalsis telescopes tumor segment)
• Pancreatic cancer: early biliary obstruction (jaundice) paradoxically improves prognosis - leads to earlier detection
• Functional endocrine tumors: β-cell adenoma < 1 cm → fatal hypoglycemia
• Ulceration → bleeding → melena (gut), hematuria (urinary tract)

Cancer Cachexia

• Definition: hypercatabolic state with loss of muscle mass (with or without fat loss), cannot be explained by diminished food intake
• Occurs in ~50% of cancer patients; most common in advanced GI, pancreatic, and lung cancers
• Responsible for ~30% of cancer deaths
• Features: extreme weight loss, fatigue, muscle atrophy, anemia, anorexia, edema
• Death: usually from atrophy of diaphragm and respiratory muscles
• Mediators: TNF, IL-1, IL-6, IFN-γ (from tumor or host immune cells)
• TNF (cachectin) suppresses appetite and stimulates lipolysis
• Proteolysis-inducing factor (PIF): tumor-derived; directly breaks down skeletal muscle
• Not simply starvation - feeding alone does NOT reverse cachexia

Paraneoplastic Syndromes

• Symptom complexes CANNOT be explained by tumor mass, invasion, metastasis, or hormones indigenous to the tumor cell of origin
• Occur in 10-15% of cancer patients
• Clinically important: may be first sign, may mimic metastasis, may be life-threatening

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16. GRADING AND STAGING

Grading

• Based on cytologic appearance (degree of differentiation)
• Premise: behavior correlates with differentiation
• Grade I (well differentiated) → Grade III/IV (poorly differentiated/anaplastic)
• Limitation: tumors are heterogeneous; single biopsy may not represent entire lesion
• Used in: prostate (Gleason score), bladder, cervix, brain

Staging

• Based on extent of disease (clinical and pathologic)
• TNM System (most widely used):
  • T = primary Tumor size (T0-T4)
  • N = regional Nodes (N0 = no involvement; N1-N3 = increasing involvement)
  • M = Metastasis (M0 = none; M1 = present)
• Greater clinical prognostic value than grading
• Requires: surgical exploration, imaging (CT, MRI, PET), sentinel lymph node biopsy

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17. LABORATORY DIAGNOSIS OF CANCER

A. Histologic and Cytologic Methods

• Gold standard: excisional biopsy with histopathology
• Frozen section: rapid intraoperative diagnosis; used for surgical margin assessment
• FNA (Fine Needle Aspiration): cost-effective, safe; distinguishes benign from malignant in accessible masses (breast, thyroid, lymph nodes); cannot assess architecture
• Cytologic smears: exfoliative cytology (Pap smear) or lavage samples
• Core needle biopsy: preserves architecture; preferred over FNA for most masses

B. Immunohistochemistry (IHC)

1. Tumor classification - cytokeratins (carcinoma), vimentin (sarcoma), S100/Melan-A (melanoma), CD markers (lymphoma)
2. Determining metastatic tumor origin - e.g., PSA for prostate, thyroglobulin for thyroid
3. Prognosis/therapy selection - ER/PR/HER2 in breast cancer (guides trastuzumab/endocrine therapy)
4. Detecting circulating tumor cells

C. Flow Cytometry

• Quantifies DNA content and cell cycle phases
• Aneuploidy detected → correlates with poor prognosis
• CD marker analysis for lymphoma/leukemia subtyping

D. Tumor Markers (Serum)

Important: Tumor markers are NOT diagnostic alone; they have limited sensitivity and specificity. Main use is monitoring response to therapy and detecting recurrence.

E. Molecular Diagnosis

• FISH (Fluorescence In Situ Hybridization): detects translocations (BCR-ABL), amplifications (HER2), deletions
• PCR/RT-PCR: detects specific gene fusions (BCR-ABL), minimal residual disease
• Next-Generation Sequencing (NGS): comprehensive mutational profiling; guides targeted therapy
• Comparative Genomic Hybridization (CGH): detects chromosomal gains and losses
• Liquid biopsy: circulating tumor DNA (ctDNA) in plasma; non-invasive; used for monitoring, resistance mutations

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18. KEY CONCEPTS SUMMARY

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