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Principles of neoplasia — nomenclature, benign and malignant features, grade and stage

A benign tumour resembles its tissue of origin, grows slowly, is circumscribed and does not metastasise, while a malignant tumour loses differentiation, invades and metastasises; the grade describes how undifferentiated the tumour looks, and the stage how far it has spread — and stage matters more for prognosis.

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Why it matters in the exam

The bank asks about names and differences. Names: a benign tumour takes the suffix "-oma" (adenoma, lipoma); malignant from epithelium — carcinoma; malignant from connective tissue — sarcoma. Exceptions: lymphoma, melanoma, seminoma and mesothelioma are malignant despite the suffix. A hamartoma is a disorganised mixture of the organ's native tissues; a choristoma is normal tissue in the wrong place; a teratoma contains tissues from three germ layers.

Signs of anaplasia: pleomorphism of cells and nuclei, hyperchromatic nuclei, a high nuclear-to-cytoplasmic ratio, many and abnormal mitoses and loss of polarity. Dysplasia is disordered growth with atypia within an epithelium; when it involves the full thickness and has not yet crossed the basement membrane — carcinoma in situ. Invasion is the most reliable sign of malignancy after metastasis, and metastasis is the absolute sign. Childhood tumours differ from those of adults: mostly embryonal, "small round blue cells", sometimes regressing spontaneously (neuroblastoma in infants), and tending to respond to treatment.

Grade is set by differentiation and sometimes by mitotic count and necrosis, in systems specific to each tumour (for example Nottingham in breast, Gleason and ISUP in prostate). Stage is set by TNM — size and extent of the primary, lymph nodes and distant metastases. The immune system responds to tumours mainly through cytotoxic CD8 T cells, and tumours escape partly through PD-L1 and loss of MHC. Paraneoplastic syndromes: the most common endocrine disorder is Cushing syndrome from ACTH secretion, mainly in small cell lung cancer, and hypercalcaemia from PTHrP is common in squamous tumours.

Key points

• Benign: differentiated, circumscribed, no metastases; malignant: anaplasia, invasion, metastases.
• Carcinoma from epithelium; sarcoma from connective tissue.
• Carcinoma in situ: full atypia without crossing the basement membrane.
• Grade = differentiation; stage = TNM; stage matters more.
• Cushing from ACTH — the most common paraneoplastic endocrine disorder.

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Sources

• Robbins and Cotran Pathologic Basis of Disease, 10th edition (2021) — Neoplasia — nomenclature, characteristics, grading and staging
• WHO Classification of Tumours Editorial Board: WHO Classification of Tumours, 5th edition, introduction, 2019–2024 — Principles of classification and grading
• Union for International Cancer Control: TNM Classification of Malignant Tumours, 9th edition (2025) — General rules

Sources are given for further reading; the text is written afresh and not copied from them.

Reviewed by the Examqo AI Professor · 2026-11-06. The text may contain errors; when in doubt, check the source.