Injection Site Fibrosarcoma
An injection site sarcoma is a tumor in the connective tissues of the cat. These tumors are called fibrosarcomas because the type of cells affected are fibroblasts. These tumors can occur at injection sites. A fibrosarcoma can develop weeks, months, or even years after a vaccination. It is likely there is a genetic predisposition to the development of these tumors. However, the exact genetic problem has not yet been identified. A surgical biopsy is often necessary to make a definitive diagnosis of injection site fibrosarcoma. Surgery is also the usual form of treatment. These tumors grow by sending finger-like projections of tumor cells among the tissues. Injection site sarcomas in cats are very difficult to treat.  Cats with tumors on the legs, where an amputation can be performed, appear to do better than cats with tumor on the trunk of the body.  Surgery can be combined with chemotherapy and radiation therapy. Most cats will never develop a vaccine associated sarcoma. Vaccines are important because they protect cats against serious diseases. The best advice is to make educated decisions about which diseases your cat should be vaccinated for.