Cancer is not a single disease. The U.S. National Cancer Institute defines it as a disease in which some of the body’s cells grow uncontrollably and spread to other parts of the body.
How cancer develops
Normal cells grow, divide and die in a controlled way. Cancer develops when genetic changes disrupt those controls. Abnormal cells may form a tumour, invade nearby tissue or travel through the blood or lymph system to form tumours elsewhere, a process called metastasis. Blood cancers such as leukaemia do not generally form solid tumours.
Benign and malignant tumours
A benign tumour is not cancer and does not invade nearby tissue or spread to distant organs, although its size or location can still cause serious problems. A malignant tumour is cancerous and can invade or spread.
Types and risk factors
Cancers are usually named for the organ, tissue or cell type where they begin. Examples include carcinomas, sarcomas, leukaemias, lymphomas and melanomas. Risk is influenced by age, inherited genetic changes, tobacco, alcohol, ultraviolet radiation, certain infections and other exposures. Having a risk factor does not mean that cancer is inevitable, and some people develop cancer without a clear preventable cause.
Diagnosis and treatment
Symptoms vary widely and often have non-cancerous causes. Persistent or unexplained changes should be assessed rather than self-diagnosed. Testing can involve imaging, laboratory tests and a biopsy, depending on the suspected cancer.
The National Cancer Institute lists surgery, chemotherapy, radiation therapy, immunotherapy, targeted therapy, hormone therapy and other approaches. The appropriate plan depends on the cancer type, stage, molecular features and individual health; no single treatment suits every cancer.
