cancer

n.

any malignant tumour, including carcinoma, lymphoma, leukaemia, and sarcoma. It arises from the abnormal, purposeless, and uncontrolled division of cells that then invade and destroy the surrounding tissues. Spread of cancer cells (metastasis) may occur via the bloodstream or the lymphatic channels or across body cavities such as the pleural and peritoneal spaces (see transcoelomic spread), thus setting up secondary tumours (metastases) at sites distant from the original tumour. Each individual primary tumour has its own pattern of local behaviour and spread; for example, bone metastasis is very common in cancers of the breast, bronchus, thyroid, kidney, and prostate but less common in other tumours.

There are many causative factors, some of which are known; for example, cigarette smoking is associated with lung cancer, radiation with some sarcomas and leukaemia, and several viruses are implicated (see oncogenic). A genetic element is implicated in the development of many cancers. In many cancers a gene called p53 is deleted or impaired: its normal function is to prevent the uncontrolled division of cells (see tumour necrosis factor). Whatever the initiating cause, cancer always results ultimately from DNA mutations.

Treatment of cancer depends on the type of tumour, the site of the primary tumour, and the extent of spread.