Bone Cancer in Dogs
Bone Cancer in Dogs
Introduction to Chemotherapy
The term “chemotherapy” describes the medications used in the treatment of cancer. These medications can be given intravenously or orally. The medications travel in the body and seek out cancer cells to destroy them. These medications are best given by veterinarians and technicians with experience in their handling and administration. Specialized staff and veterinarians are also familiar with the potential side effects and monitoring that should be done.
To find an oncologist in your area, ask your primary veterinarian, call the nearest veterinary teaching hospital in your area, or contact either the American College of Veterinary Internal Medicine or the Veterinary Cancer Society.
In the treatment of bone cancer, chemotherapy is usually prescribed in addition to other treatments, most commonly amputation. The traditional approach is to perform amputation first, then follow up with the chemotherapy. This approach has the highest survival rate of all treatment options for managing bone cancer, based on currently accepted statistics. Depending on the oncologist and the overall health of the dog, the chemotherapy may be administered immediately after surgery, or within two weeks of the surgery.
Chemotherapy is administered after amputation to catch any stray cancer cells that may have already traveled through the blood to other areas. In bone cancer, these stray cells travel most commonly to the lungs, creating the potential for metastases. The cells themselves are not visible on x-rays. Because the medications also travel in the blood, they can find these cells and kill them before they become visible metastases.
Practically all anti-cancer drugs have side effects. However, their potential effect against the cancer outweighs the possible side effects. Although serious adverse effects can occur with any chemotherapy, there is less than a 5 percent chance your pet will be hospitalized with side effects and less than a 1 percent chance of fatality.
Most dogs handle chemotherapy very well. The most common side effects are nausea, vomiting, change in appetite and diarrhea. These side effects usually last for several days and can be minimized or avoided altogether with medications prescribed by your oncologist. Most doctors will also advise not to feed your pet on the morning of the treatment. The chemotherapy sessions can last several hours or possibly all day. Blood work and urine tests are usually done before the chemotherapy is administered and should be checked in between cycles as well. Occasionally the chemotherapy can affect the white blood cell count or liver/kidney functions, which is why monitoring is so important.
The most commonly used chemotherapy medications used for management of bone cancer are cisplatin, carboplatin and adriamycin, also known as doxorubicin. Some protocols use a single agent in multiple doses several weeks apart; others use combination therapy, rotating two drugs several weeks apart. The chemotherapy is given in cycles to provide the most exposure to different cancer cells as they are multiplying. Combination chemotherapy works in different ways and allows for cells to be destroyed at different stages in their cycle.
There is also another type of chemotherapy protocol, called the metronomic protocol. This protocol combines several medications including cyclophosphamide, an oral chemotherapy drug. These medications work on slowing down the blood supply to cancer cells, and also slow down their growth. The principle behind this is called “anti-angiogenesis” (angiogenesis means “creation of blood”). The metronomic protocol is usually used once the metastases are visible either on x-ray or exam, or in some cases where amputation is not an option.