Key points
- A neoplasm is abnormal, uncontrolled growth that persists after the stimulus that started it has gone.
- Malignant tumours invade and metastasise; benign tumours do not.
- Carcinomas come from epithelium, sarcomas from connective tissue.
- Carcinoma in situ has not crossed the basement membrane, so it cannot yet spread.
Neoplasia
A neoplasm (“new growth”) is a mass of cells growing without the normal controls, and growing on after whatever triggered it has been removed. A tumour is simply a swelling, though in practice the words are used interchangeably. Cancer means a malignant neoplasm.
Benign or malignant?
| Feature | Benign | Malignant |
|---|---|---|
| Growth | Slow | Often rapid |
| Differentiation | Looks like the tissue of origin | Ranges from well to poorly differentiated (anaplastic) |
| Edge | Well defined, often encapsulated | Irregular, infiltrating |
| Invasion | None | Invades surrounding tissue |
| Metastasis | Never | Can spread to nodes and distant organs |
| Harm | From size or position, or hormone production | From invasion, spread and systemic effects |
How tumours are named
- Benign: tissue + -oma: adenoma (glands), lipoma (fat), leiomyoma (smooth muscle), fibroadenoma.
- Carcinoma: malignant tumour of epithelium: adenocarcinoma (glandular), squamous cell carcinoma, transitional cell (urothelial) carcinoma. About 85–90% of cancers.
- Sarcoma: malignant tumour of connective tissue: liposarcoma, leiomyosarcoma, osteosarcoma.
- Haematological: lymphoma, leukaemia, myeloma.
- Others: germ cell tumours (seminoma, teratoma), neuroendocrine tumours, melanoma, gastrointestinal stromal tumour (GIST).
Watch the exceptions
Melanoma, lymphoma and seminoma end in -oma but are malignant.
From normal to invasive: a stepwise process
Hyperplasia (more cells) → metaplasia (one mature cell type replaced by another, as in Barrett’s oesophagus) → dysplasia (disordered growth, graded low or high) → carcinoma in situ (full-thickness change that has not crossed the basement membrane) → invasive carcinoma. Each step usually needs further genetic damage: the colorectal adenoma–carcinoma sequence is the classic example (see cancer genetics).
The hallmarks of cancer
Hanahan and Weinberg described the capabilities a cell acquires on the way to cancer:
- Sustaining its own growth signals
- Ignoring growth-suppressing signals
- Resisting cell death (apoptosis)
- Unlimited replication (telomerase)
- Making new blood vessels (angiogenesis)
- Invading and metastasising
- Reprogramming energy metabolism
- Evading the immune system
Two features enable them: genome instability and tumour-promoting inflammation. Many modern drugs target a hallmark: anti-VEGF drugs block angiogenesis, and checkpoint inhibitors undo immune evasion.
What causes cancer?
- Chemicals: tobacco (the biggest single cause), alcohol, aflatoxin, occupational carcinogens.
- Infections: H. pylori (gastric cancer and MALT lymphoma), HPV (cervix, anus, oropharynx), hepatitis B and C (liver), EBV.
- Radiation: ultraviolet light (skin), ionising radiation.
- Obesity and inactivity: colorectal, oesophageal adenocarcinoma, endometrial, breast after menopause.
- Inherited genes: about 5–10% of cancers (see inherited syndromes).
How cancer presents
- Local: a lump, an ulcer, bleeding, obstruction (dysphagia, bowel obstruction, jaundice), pain.
- Spread: nodes, liver, lung, bone, brain, peritoneum.
- Systemic: weight loss, fatigue, fever, anaemia.
- Paraneoplastic: hypercalcaemia (PTHrP), hyponatraemia (SIADH), Cushing’s (ectopic ACTH), migratory thrombophlebitis.
Frequently asked questions
What is the difference between a benign and a malignant tumour?
A malignant tumour invades surrounding tissue and can spread (metastasise) to lymph nodes and distant organs. A benign tumour does neither, although it can still cause harm by its size, position or hormone production.
What is the difference between a carcinoma and a sarcoma?
A carcinoma arises from epithelium and accounts for about 85 to 90% of cancers. A sarcoma arises from connective tissue such as fat, muscle or bone.
What is carcinoma in situ?
Full-thickness malignant change in an epithelium that has not crossed the basement membrane, so it cannot yet spread.
Further reading
- Hanahan D, Weinberg RA. Hallmarks of cancer: the next generation. Cell 2011;144:646–74.
- Hanahan D. Hallmarks of cancer: new dimensions. Cancer Discov 2022;12:31–46.