The goal of a surgical intervention in cancer treatment is to remove or reduce the primary cancerous tumor and allow either chemotherapy or radiation therapy to be more effective.
Before surgery is performed, your veterinarian will run tests to ensure your dog can tolerate the surgery. Therefore, blood tests and frequently x-rays of the lungs or other parts of the body will be run to determine the dog's overall health and to determine if the cancer has spread. In certain cases, chemotherapy or radiation therapy might be recommended before surgery in order to shrink the tumor so it can be removed more easily.
The first surgical procedure is frequently the most critical because it has the opportunity to cure the cancer. When a surgeon needs to operate a second or third time, they will be dealing with scar tissue and aggravation of tumor cells. Therefore, the veterinarian will make a large incision on the first pass in order to get "clean margins". This means that a wide area of normal tissue around the tumor will be removed so that no cancer cells can be detected under a microscope from the margins of the tissue extracted.
In addition to trying to get enough tissue extracted with clean margins, any nearby enlarged lymph nodes will also be removed. This is because the lymphatic system can carry cancer cells to other parts of the body.
The reasons for surgery are varied. Sometimes it is believed that the cancer can be totally removed and your dog be cured of cancer. However, that is not always the case. Sometimes surgery is performed for palliative or comfort reasons because the cancer symptoms are decreasing the quality of the dog's life. Palliative surgery is frequently performed in dogs with osteosarcoma (bone cancer) by amputating a limb,
or a spleen removed in dogs with hemangiosarcoma in order to prevent internal bleeding.
Another surgical technique frequently used is debulking. Debulking is surgery to reduce a large tumor
so that chemotherapy or radiation therapy has a better chance of working. If chemotherapy is to be administered after surgery, there is often a waiting period of 7-12 days in order to allow the dog to recover fully from surgery before undergoing that treatment. My dog Puma was put on an osteosarcoma clinical after his leg was amputated to determine if there was a difference in outcome for dogs who received chemotherapy the day after surgery vs. waiting a week. He was in the group surgery that received chemotherapy agents directly after surgery but he did not outlive the average. In fact, the veterinarian running the trial told me after the study ended that there wasn't any statistically significant advantage to giving chemotherapy post surgery vs. waiting a week in this particular study.
Radiation therapy may also be used post-surgery. Like chemotherapy, there may be a waiting period after the surgery or it may start immediately, depending upon the type of cancer. Again, the goal is to either further shrink the primary tumor if it wasn't completely removed surgically or to treat secondary sites.