Chemotherapy is the treatment of cancer with drugs that can destroy cancer cells. Chemotherapy drugs interfere with cell division in various possible ways, e.g. with the duplication of DNA or the separation of newly formed chromosomes. Most forms of chemotherapy target all rapidly dividing cells and are not specific to cancer cells, although some degree of specificity may come from the inability of many cancer cells to repair DNA damage, while normal cells generally can. Hence, chemotherapy has the potential to harm healthy tissue, especially those tissues that have a high replacement rate. These cells usually repair themselves after chemotherapy.

Some drugs work better together than alone, so two or more drugs are often given at the same time. This is called combination chemotherapy, most chemotherapy regimens are given in a combination.

The treatment of some leukaemias and lymphomas requires the use of high-dose chemotherapy, and total body irradiation (TBI).