Neoplasia — Basic Concepts
Pathology · Neoplasia · lean revision notes
Neoplasia — Basic Concepts
Neoplasia ("new growth") is an abnormal, autonomous, uncoordinated proliferation of cells that persists even after the inciting stimulus is withdrawn. This chapter builds the vocabulary of oncology — nomenclature, the benign-versus-malignant divide, anaplasia, grading versus staging, and the biology of invasion and metastasis — the foundation on which all of NEET PG pathology of cancer rests.
High-yield: Willis' classic definition — "A neoplasm is an abnormal mass of tissue, the growth of which exceeds and is uncoordinated with that of normal tissue, and persists in the same excessive manner after cessation of the stimulus which evoked the change." The keyword is persistence/autonomy.
Definition & basic vocabulary
Every tumour has two basic components:
- Parenchyma — the transformed/neoplastic cells. This determines the biological behaviour and gives the tumour its name.
- Stroma — non-neoplastic, host-derived connective tissue, blood vessels and (variably) inflammatory cells. The stroma is essential for blood supply (angiogenesis).
- A tumour with abundant collagenous stroma is desmoplastic / scirrhous (classically infiltrating duct carcinoma of breast — stony-hard).
- "Tumour" literally means swelling; in oncology it is used synonymously with neoplasm.
- Oncology = study of tumours; -oma = the usual suffix for a neoplasm.
Nomenclature
Naming is the single most testable part of this topic. The rules differ for benign and malignant tumours.
Benign tumours
Generally named by adding -oma to the cell of origin.
| Tissue of origin | Benign tumour |
|---|---|
| Fibrous tissue | Fibroma |
| Fat | Lipoma |
| Bone | Osteoma |
| Cartilage | Chondroma |
| Smooth muscle | Leiomyoma |
| Skeletal muscle | Rhabdomyoma |
| Blood vessels | Haemangioma |
| Glandular epithelium | Adenoma |
| Epithelium forming finger-like projections | Papilloma |
| Glandular epithelium with cystic spaces | Cystadenoma |
Malignant tumours
- Carcinoma — malignancy of epithelial origin (all three germ layers can give rise to epithelium).
- Glandular pattern → adenocarcinoma
- Squamous pattern → squamous cell carcinoma
- Sarcoma — malignancy of mesenchymal / connective tissue origin (e.g., fibrosarcoma, liposarcoma, osteosarcoma, leiomyosarcoma).
High-yield: Carcinoma = epithelial; Sarcoma = mesenchymal. Carcinomas spread chiefly via lymphatics; sarcomas chiefly via blood (haematogenous).
| Feature | Carcinoma | Sarcoma |
|---|---|---|
| Origin | Epithelium | Mesenchyme |
| Common age | Older adults | Often younger |
| Frequency | Common | Rare |
| Tumour markers | Epithelial (cytokeratin, EMA) | Vimentin |
| Preferred spread | Lymphatic | Haematogenous |
| Cellular cohesion | Cohesive nests (cell adhesion molecules) | Often non-cohesive |
Important exceptions ("-oma" that are actually malignant)
These trip up candidates frequently.
High-yield exceptions: Lymphoma, melanoma, mesothelioma, seminoma, hepatoma (hepatocellular carcinoma), glioma, and the "blastomas" (neuroblastoma, retinoblastoma, nephroblastoma, medulloblastoma, hepatoblastoma) are all malignant, despite the -oma suffix.
Special / named entities
- Teratoma — arises from totipotent germ cells; contains tissues from all three germ layers (ectoderm, mesoderm, endoderm). Ovarian mature cystic teratoma (dermoid cyst) is benign; most testicular teratomas in adults are malignant.
- Mixed tumour (pleomorphic adenoma) — salivary gland (parotid), single clone differentiating into epithelial + myxoid/cartilaginous tissue.
- Hamartoma — disorganised but mature, indigenous tissue native to the site (e.g., pulmonary hamartoma, Peutz–Jeghers polyps). It belongs there but is jumbled.
- Choristoma — heterotopic rest of normal tissue at an abnormal/foreign site (e.g., pancreatic tissue in stomach wall, gastric mucosa in Meckel's diverticulum).
High-yield mnemonic: "Hamartoma = Home tissue (right place, wrong arrangement); Choristoma = Change of place (normal tissue, wrong location)."
Misleading misnomers
- Lymphangioma vs lymphoma — former benign, latter malignant.
- Granuloma, tuberculoma, hamartoma, choristoma — not true neoplasms.
Benign vs malignant — the four pillars
The distinction rests on differentiation/anaplasia, rate of growth, local invasion, and metastasis.
| Characteristic | Benign | Malignant |
|---|---|---|
| Differentiation | Well differentiated; resembles tissue of origin | Variable; some lose differentiation (anaplasia) |
| Rate of growth | Slow; mitoses few & normal | Erratic, often rapid; mitoses many & atypical |
| Local invasion | Cohesive, encapsulated, expansile | Infiltrative, invasive, no capsule |
| Metastasis | Absent | Present (hallmark of malignancy) |
| Nuclei | Normal N:C ratio | High N:C ratio (~1:1) |
| Necrosis / haemorrhage | Rare | Common (outgrows blood supply) |
High-yield: Metastasis is the single most reliable feature that unequivocally marks a tumour as malignant. No benign tumour metastasises.
Anaplasia & cellular features of malignancy
Anaplasia = "to form backward" — lack of differentiation; the morphological hallmark of malignant transformation. Anaplastic cells show:
- Pleomorphism — variation in size and shape of cells and nuclei.
- Nuclear hyperchromasia — dark, coarse, clumped chromatin.
- High N:C ratio approaching 1:1 (normal ~1:4 to 1:6).
- Prominent / large nucleoli.
- Abnormal (atypical, tripolar, quadripolar) mitoses — highly suggestive of malignancy.
- Loss of polarity — disorganised, haphazard architecture.
- Tumour giant cells with one large/multiple nuclei.
Related terms to keep straight:
- Dysplasia — disordered but non-neoplastic growth, principally in epithelium; loss of uniformity and architectural orientation. Graded mild → moderate → severe.
- Carcinoma in situ (CIS) — severe dysplasia involving the full thickness of epithelium but basement membrane intact (no invasion). Pre-invasive stage.
- Metaplasia — reversible replacement of one differentiated cell type by another (e.g., Barrett oesophagus: squamous → columnar).
High-yield: Dysplasia does not always progress to cancer and may be reversible if the inciting stimulus (e.g., smoking, HPV) is removed. CIS, by definition, has an intact basement membrane.
Grade vs Stage — a perennial favourite
| Grade | Stage | |
|---|---|---|
| Based on | Degree of differentiation & mitotic activity (microscopic) | Extent of spread (anatomic) |
| Assesses | How the tumour looks | How far the tumour has gone |
| Systems | GX, G1–G4; Broders' grading | TNM; AJCC; Dukes (colon); FIGO (gynae) |
| Prognostic value | Useful | Superior — stage is the more important prognostic factor |
- TNM: T = primary tumour size/extent, N = regional lymph node involvement, M = distant metastasis.
- Higher grade = poorly differentiated = more anaplastic = worse.
High-yield: Between grade and stage, STAGE has greater clinical/prognostic value in most solid tumours.
Stepwise approach to a tumour report: Identify tissue of origin → benign or malignant? → if malignant, assign grade (differentiation) → then stage (TNM/spread) → plan management.
Invasion & Metastasis
Metastasis = development of secondary implants discontinuous from the primary tumour. It is the defining property of malignancy and the major cause of cancer death.
The metastatic cascade (invasion–metastasis cascade)
- Loosening of intercellular junctions — down-regulation of E-cadherin.
- Degradation of basement membrane & ECM — matrix metalloproteinases (MMPs), type IV collagenase.
- Attachment to ECM components (laminin, fibronectin receptors).
- Migration / locomotion — autocrine motility factors, cleavage products as chemoattractants.
- Intravasation into vessels.
- Embolisation & survival in circulation (tumour cell + platelet emboli evade immune attack).
- Extravasation & arrest at distant site.
- Colonisation — growth of secondary deposit; angiogenesis (VEGF) essential.
High-yield: Loss of E-cadherin is the key early step that loosens tumour cells. MMPs / type IV collagenase degrade the basement membrane. VEGF drives the tumour angiogenesis necessary for both primary growth and metastatic colonisation.
Routes of spread
| Route | Typical tumours | Examples / notes |
|---|---|---|
| Lymphatic | Carcinomas | Breast Ca → axillary nodes; "sentinel node" is the first draining node |
| Haematogenous | Sarcomas, RCC, HCC, follicular thyroid, choriocarcinoma | Liver & lung are commonest sites (drain via portal & caval systems) |
| Transcoelomic / seeding | Ovarian Ca, GI Ca | Krukenberg tumour, peritoneal carcinomatosis |
| Along epithelium-lined cavities | — | CSF spread of medulloblastoma |
| Implantation | Iatrogenic | Surgical/needle tract seeding |
High-yield: Carcinomas → lymphatic; Sarcomas → haematogenous (the classic exam dichotomy). But note key carcinomas that love the bloodstream: renal cell carcinoma, hepatocellular carcinoma, follicular thyroid carcinoma, and choriocarcinoma.
- Krukenberg tumour — bilateral ovarian metastasis (classically from gastric signet-ring cell carcinoma) via transcoelomic spread.
- Virchow's node (Troisier sign) — left supraclavicular node, from gastric/abdominal carcinoma.
- Sister Mary Joseph nodule — periumbilical metastatic deposit.
- Blumer's shelf — rectal-shelf metastasis felt on PR.
Sites of metastasis
- Most frequent organs receiving metastases: liver and lung (largest capillary beds).
- Cancers that commonly metastasise to bone: Breast, Lung, Thyroid, Kidney, Prostate — mnemonic "BLT with a Kosher Pickle".
- Osteoblastic (sclerotic) bone mets → classically prostate; osteolytic → most others.
Organs notably spared by metastasis
High-yield: Skeletal muscle and spleen are relatively resistant to metastatic deposits despite rich blood supply (the "metastasis paradox"). Seed-and-soil hypothesis (Paget) explains organ tropism.
Cancer epidemiology in India
- Overall commonest cancer in Indian women: breast cancer (it has overtaken cervical cancer nationally), with cervical cancer still leading in many rural regions.
- Commonest cancer in Indian men: oral cavity / lung (strongly tied to tobacco — gutkha, bidi, smoking). Tobacco-related cancers dominate Indian male cancer burden.
- Tobacco is the single largest preventable cause of cancer in India.
- Globally, lung cancer is the leading cause of cancer death.
High-yield: In India, tobacco-related cancers (oral cavity, lung, oesophagus) lead in men; breast and cervix lead in women. Cervical cancer is linked to HPV 16 & 18.
Recently asked / exam angle
- "Carcinoma vs sarcoma — which spreads by lymphatics?" → Carcinoma.
- "Tissue at the wrong site but otherwise normal" → Choristoma (vs hamartoma = right site, jumbled).
- "Most reliable feature of malignancy" → Metastasis.
- "Best prognostic indicator — grade or stage?" → Stage.
- "Krukenberg tumour primary site" → Stomach (signet-ring adenocarcinoma).
- "Molecule lost early in invasion" → E-cadherin; "enzyme degrading BM" → type IV collagenase / MMP.
- Identify malignant "-oma": seminoma, melanoma, lymphoma, mesothelioma, hepatoma are malignant.
- "Carcinoma in situ — basement membrane status?" → Intact.
- Image-based: atypical tripolar mitosis / marked nuclear pleomorphism → feature of anaplasia/malignancy.
- "Tumour spreading transcoelomically" → ovarian carcinoma.
- Sites resistant to metastasis → spleen & skeletal muscle.
Rapid revision
- Willis definition — neoplasia = autonomous growth persisting after stimulus stops.
- Parenchyma names the tumour; stroma (host) supplies blood — desmoplastic stroma = scirrhous (breast Ca).
- Carcinoma = epithelial; Sarcoma = mesenchymal. Carcinoma → lymph; sarcoma → blood.
- Malignant "-omas": lymphoma, melanoma, mesothelioma, seminoma, hepatoma, glioma, blastomas.
- Hamartoma = home tissue, disorganised; Choristoma = ectopic normal tissue.
- Teratoma = all three germ layers (germ cell origin).
- Metastasis = the one feature that proves malignancy; no benign tumour metastasises.
- Anaplasia hallmarks: pleomorphism, hyperchromasia, high N:C ratio (~1:1), atypical mitoses, loss of polarity.
- CIS = full-thickness dysplasia with intact basement membrane (pre-invasive).
- Grade = differentiation; Stage = spread; stage is the better prognostic factor (TNM).
- Invasion cascade: ↓E-cadherin → MMP/type IV collagenase → migration → intravasation → VEGF-driven colonisation.
- Krukenberg = bilateral ovarian met from gastric signet-ring Ca; bone mets — Breast, Lung, Thyroid, Kidney, Prostate; spleen & skeletal muscle spared. India: tobacco cancers in men, breast/cervix in women.