It has been discovered that cats can develop a vaccine related fibrosarcoma (a cancer of fibrous tissues such as muscle). Studies done in the past several years have shown an association of a soft tissue sarcoma at the vaccine sites such as rabies and feline leukemia (FeLV). These studies have shown that the appearance of these fibrosarcomas is between 4 weeks to 10 years post vaccine. It also determined that no single vaccine manufacturer or vaccine type can be associated with this type of cancer. Although the mechanism that causes the cancer to develop is not actually known, it is thought that the inflammatory reaction is why the tumor will develop at a later date.
Vaccine related fibrosarcoma will appear as a lump at the vaccine site. A CT scan (Computed Tomography), also known as Cat Scan or an MRI (Magnetic Resonance Imaging) may be needed to evaluate the extent of the cancer to help determine a proper treatment. Surgery is recommended to remove the tumor plus the surrounding healthy tissues. There must be a wide margin (2 to 3 cm all around) plus underneath the tumor removed as this is an aggressive cancer. If the healthy tissue is not removed, the incidence of reoccurrence is high and the cancer can reoccur within 2 to 3 months. Due to the fact that 50 of these tumors will reoccur, the first surgery is the best way of removing the entire tumor. This is a major surgery and should be done by a board certified surgeon. If the tumor is on a limb, the usual course of action is amputation. Although many owners are hesitant to have a three legged pet, the animals do quite well with three legs.
Keep in mind that, although the surgery will remove the visible tumor, cancer cells can be left behind. To kill the remaining cancer cells, radiation therapy may be used. The timing of the radiation therapy will depend upon the individual veterinarian, oncologist and / or surgeon but it may within two weeks post surgery. Using chemotherapy on the vaccine related fibrosarcoma may or may not have any benefits for the patient as it does not appear to affect the cats overall survival. However, it may delay the time that the tumor will reoccur.
As with all cancers, especially when cats are receiving radiation and / or chemotherapy, weight loss can occur. This is usually due to loss of appetite or general feeling of illness due to the side effects of the cancer treatment. It is important to have sufficient nutritional support to reduce the post surgical complications and help the healing process.
The prognosis for cats by surgery alone is poor while cats that have received surgery plus radiation and /or chemotherapy improve with a higher survival rate. If you notice a lump on or close to a site where a vaccine has been given, it is important to call your veterinarian and speak to the veterinary assistant to schedule an appointment or for a referral to a board certified surgeon for a definite diagnosis.