Cancer

The term cancer covers many diseases rather than one condition. In healthy tissues, cell growth and cell death are regulated; cancer develops when abnormal cells evade some of these controls, multiply, and can invade nearby tissues. Cells that break away from a primary tumour may travel through the blood or lymphatic system and form tumours elsewhere, a process called metastasis. Many cancers form solid tumours, but blood cancers such as leukaemia generally do not. A tumour is not automatically cancer: benign tumours do not invade or spread in the way malignant tumours do, though some benign growths can still cause serious problems.

Cancers may be named for the organ or tissue where they begin, or grouped by their cell of origin. Broad categories include carcinomas, which arise in epithelial tissues; sarcomas, which develop in connective or supporting tissues; leukaemias, which affect blood-forming tissues; lymphomas and myelomas, which arise in cells of the immune system; and cancers of the brain and spinal cord. The biological changes behind cancer differ, but often involve alterations in genes that normally regulate cell growth, cell division or DNA repair. Some changes are inherited; others accumulate during life, including through errors in cell division or exposure to cancer-causing agents. For many individuals, it is not possible to identify one exact cause.

Cancer risk depends on the cancer type and reflects a combination of factors. Age, family history, some inherited mutations, tobacco, alcohol, ultraviolet and ionizing radiation, certain infections, and some workplace or environmental exposures are among the factors associated with particular cancers. Risk factors change probabilities; their presence does not mean that a person will develop cancer, and many diagnoses cannot be explained by a single exposure. Prevention can reduce some risks—for example, avoiding tobacco and protecting against certain cancer-causing infections—but cannot prevent every cancer. Early diagnosis seeks to identify cancers in people who have symptoms. Screening instead tests people without symptoms and is useful only for selected cancers and populations where evidence shows benefits outweigh potential harms, such as false results and overdiagnosis.

Evaluation may combine a person's history and examination with laboratory tests, imaging and examination of a tissue sample. A biopsy and pathology assessment can identify the cancer type and features that help guide care; blood tests or imaging alone do not establish every diagnosis. For many solid cancers, staging describes the primary tumour, nearby lymph nodes and whether disease has spread, although systems differ and some blood and brain cancers use other approaches. Treatment is chosen according to the cancer, its stage and characteristics, the person's health and preferences, and available services. It may involve surgery, radiotherapy, chemotherapy, hormone therapy, immunotherapy or targeted medicines, alone or in combination. Supportive and palliative care can address symptoms and quality of life during cancer care; it is not limited to a single treatment stage.

Cancer affects people, families and health systems worldwide, but the burden and outcomes vary substantially among countries and among cancer types. Effective prevention, timely diagnosis, treatment and survivorship support depend on access to trained health workers, diagnostic services, medicines and follow-up care. International agencies such as the World Health Organization and the International Agency for Research on Cancer assess evidence about cancer risks and support public-health planning. Population-level policy therefore complements individual clinical care, while research continues to improve understanding, prevention and treatment.