Surgery is the treatment that's most likely to be curative. Surgery removes the cancer from the body. For example, if your pet is diagnosed with a cancer of the jaw, removing the affected portion of the bone before the cancer metastasizes is curative because the cancer is gone. Surgery is only curative if the cancer hasn't spread, or if the other affected areas can be removed surgically. Obviously for something like cancer of the white blood cells, or leukemia, surgery won't work because that cancer can't be cut out.
Radiation therapy is another treatment option.
Radiation can work well on a local area of cancer that either can't be treated surgically, or was treated surgically and some of the cancer remains in the tissue. An example where radiation is a good treatment choice is in a tissue that had a tumor removed but the cancer had spread to the local lymph nodes. The radiation can be focused on the lymph nodes and spare the rest of the tissues and organs. Radiation works by harming rapidly dividing cells. When irradiated, cancer cells can't divide and spread, so they die.