It really depends on the type of cancer you have. Cancer of the knee can be one of multiple types - but most commonly it is related to cancer of the bones around the knee. Depending on the severity, tumor removal through surgery followed by radiation or chemotherapy is the course.
Now a days new treatments are available to control cancer. Usually the amputation is done to prevent the cancer from spreading. But sometime chemotherapy is also given for better result. However the siddha medicines will help you to live long but with pain. Therapists may help to reduce the effect.
As with most cancers, the standard treatment would be chemotherapy, surgery and radiation. Hopefully the chemotherapy could be given in advance to try to reduce the size of the offending tumor so that less tissue may need to be excised while still obtaining clear margins.