Neoplasia Fundamentals
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Direct answer
A neoplasm is an abnormal tissue mass whose growth exceeds normal tissue and persists after the stimulus withdraws. Benign tumours are well differentiated, slow, encapsulated and non-metastasising; malignant tumours show variable differentiation, rapid growth, local invasion and metastasis — invasion and metastasis being the two most reliable discriminators. Nomenclature follows tissue of origin with -oma for benign and -carcinoma or -sarcoma for malignant tumours, but high-yield exceptions break the rules and FMGE tests them directly.
What you must remember
- Benign epithelial tumours: adenoma, papilloma, cystadenoma; malignant counterparts: adenocarcinoma and squamous or transitional carcinoma.
- Mesenchymal: lipoma, fibroma, chondroma, osteoma and haemangioma are benign; their malignant counterparts are sarcomas such as osteosarcoma and rhabdomyosarcoma.
- Malignant despite the -oma suffix: lymphoma, leukaemia, seminoma, melanoma, mesothelioma and hepatoma (hepatocellular carcinoma). Teratoma is benign in the ovary (dermoid) but usually malignant in the testis.
- Special names: pleomorphic adenoma is the salivary mixed tumour; blastomas are childhood malignant tumours (neuroblastoma, Wilms); a hamartoma is disorganised native tissue, a choristoma normal tissue at an abnormal site.
- Terminology: anaplasia means loss of differentiation with pleomorphism and abnormal mitoses; dysplasia progresses from basal-third disorder to carcinoma in situ, where atypia fills the epithelium behind an intact basement membrane.
- Grading is histological aggressiveness; staging (TNM — tumour, nodes, metastases) is anatomical extent and generally the stronger prognostic determinant.
- Spread: lymphatic for carcinomas, haematogenous for sarcomas and for renal, hepatic, thyroid and choriocarcinomas that invade veins; transcoelomic spread giving Krukenberg ovarian deposits from gastric signet-ring carcinoma; CSF seeding by medulloblastoma.
Common confusion
Carcinoma in situ versus invasive carcinoma is the key boundary — an intact basement membrane confines disease and offers cure, while breach defines invasion and opens spread routes. Seminoma and melanoma are malignant despite their suffix, and a signet-ring ovarian deposit signals a gastric primary rather than an ovarian cancer. Distinguish metastasis, which reproduces the parent histology, from a second primary tumour.
Exam-focused takeaway
FMGE asks nomenclature as matching questions and spread as scenarios — a gastric cancer with bilateral ovarian masses (Krukenberg), a posterior fossa tumour with spinal deposits (medulloblastoma CSF seeding). Hamartoma versus choristoma and grading versus staging appear as single-liners; the naming exceptions are the cheapest marks in the paper.
Frequently asked questions
Why are invasion and metastasis the best malignancy criteria?
Differentiation and growth rate overlap between benign and malignant tumours, whereas basement-membrane breach and distant growth are definitive malignant behaviour. Reactive atypia alone never metastasises.
What is a Krukenberg tumour?
A bilateral ovarian metastasis of signet-ring cells, classically from a gastric adenocarcinoma spreading across the peritoneum. The primary may be clinically silent and must be sought.
Name two malignant tumours ending in -oma.
Lymphoma and melanoma; seminoma, mesothelioma and hepatocellular carcinoma are others. These exceptions are standard examination fare.
How do dysplasia and metaplasia differ?
Metaplasia is reversible substitution of one mature cell type for another, such as squamous change in smokers, without atypia. Dysplasia adds cytological atypia and disordered architecture and can progress to carcinoma in situ.
What does TNM staging measure?
Anatomical extent — primary tumour size and depth, regional node involvement and distant metastases. It guides treatment and predicts outcome better than histological grade in most cancers.
Hamartoma versus choristoma — what is the difference?
A hamartoma is disorganised overgrowth of cells normal for the site, such as a pulmonary hamartoma; a choristoma is normal tissue in the wrong place, such as pancreatic tissue in the stomach wall.