Chemotherapy is treatment of a disease or medical condition with chemicals that attack the cause of the medical condition. The term is most commonly used to describe treatment of cancer with anticancer drugs. Chemotherapy destroys cancer cells in a tumor. It can also kill cancer cells that have broken off from the main tumor and traveled through the blood or lymph systems to spread (metastasize) to other parts of the body.

Scientists have explored the use of chemicals to treat cancer since the mid-nineteenth century. The sex hormones estrogen and androgen were first used to treat breast and prostate cancer in 1945, and a year later, the first chemotherapy drug developed specifically to treat cancer was introduced by American scientist Cornelius Rhoads.

Today, more than 50 chemotherapy drugs are available to treat cancer and many more are under development. Most chemotherapy drugs interfere with the ability of cells to grow...