Chemotherapy is any treatment involving the use of drugs to kill cancer cells. Cancer chemotherapy may consist of single drugs or combinations of drugs, and can be administered through a vein, injected into a body cavity, or delivered orally in the form of a pill. Chemotherapy is different from surgery or radiation therapy in that the cancer-fighting drugs circulate in the blood to parts of the body where the cancer may have spread and can kill or eliminate cancers cells at sites great distances from the original cancer. As a result, chemotherapy is considered a systemic treatment.More than half of all people diagnosed with cancer receive chemotherapy. For millions of people who have cancers that respond well to chemotherapy, this approach helps treat their cancer effectively, enabling them to enjoy full, productive lives. Furthermore, many side effects once associated with chemotherapy are now easily prevented or controlled, allowing many people to work, travel, and participate in many of their other normal activities while receiving chemotherapy.