Surgery, radiation, chemotherapy, and, for some cancers, hormones or hormone-blocking medications are all used to treat cancer. The goal of cancer treatment is to kill cancerous cells while killing as few healthy cells as possible in the process.

Surgery is used to remove cancer cells that are packed together. Half of all cancers are treated with surgery. Surgeons will also remove normal cells around the cancerous cells or tumour to determine if the cancer has spread. Once the cancer has spread, it's very difficult to remove cancer cells with surgery.

Radiation is used to treat localized cancers. Radiation therapy can take a number of different forms. A beam of radiation can be aimed onto the skin near the site of the cancer. The radiation kills the cancer cells. Unfortunately, it also kills healthy cells. Newer radiation machines are getting better at focusing the radiation only on the cancerous cells, and not the normal cells. Radioactive particles can also be injected into the blood. The particles stick to cancerous cells, but not to normal cells. Sometimes, small radioactive particles are placed into or near the cancer, giving the cancerous cells a much higher dose of radiation than the normal cells (this is called brachytherapy).

Chemotherapy is treatment that uses anticancer medications. It's often used when the cancer has spread into the bloodstream. For many cancers, a combination of medications is used because it works better than just one medication. A complete response to chemotherapy is when all detectable cancer has disappeared. However, some cancer cells may still remain in the body undetected. As a result, the cancer may grow back after a period of remission. A partial response is when the cancer shrinks by more than half. Unfortunately, many cancers become immune to the anticancer medications over time. There are certain types of cancers (e.g., breast cancer, prostate cancer) that are influenced by hormones; they can be treated with hormones or hormone-blocking medications to slow their growth.

Genetic engineering is being used to control the genes that turn cancer growth on and off and to control the enzymes that allow cancer cells to continually divide and grow. Cancer vaccines, antibodies combined with poisons, and chemicals that turn off blood vessel growth in cancers, are some of the newer developments being investigated in the battle against cancer.