Chemotherapy is the use of chemicals to treat any disease, but the term has come to be applied most commonly to the use of drugs to treat cancer and that exhibit cytotoxic activity through inhibition of cell division. Recently, several other classes of drugs (biologicals) started to be used to treat cancer, often in conjunction with conventional chemotherapy. Cancer is an abnormal growth or proliferation of cells that tends to invade locally or spread to distant parts of the body. Several treatment modalities can be used for cancer. Surgery physically removes the abnormal growth, whereas radiation, immunotherapy, hormonal therapy, and chemotherapy are directed at killing or slowing the growth of cancerous cells.