A swelling, nodule or mass under your cat's skin in a region of the body that was previously used for injection or vaccination should be taken very seriously. If this occurs, you should schedule an appointment with your veterinarian to have your cat examined and the mass evaluated. This approach is recommended especially if the mass has persisted for 3 or more months, is larger than 2 cm (just under one inch) in diameter, or if you notice that the mass has been increasing in size during the one month after injection or vaccination. Have your veterinarian examine your cat as soon as possible in this situation.
Diagnostic tests are needed to recognize injection-site sarcomas and exclude other diseases. A complete medical history and thorough physical examination. An injection-site sarcoma is suspected based on a history of vaccination (or other injection) in the location on the cat's body in which the tumor has been identified.
Fine needle aspirate. A fine needle aspirate inovles placing a needle into the mass and sucking back tumor cells. The cells are injected onto a microscope slice and examined. This can help identify the tumor type to help determine the stage of the tumor and the treatment recommendations. Fine needle aspiration not considered reliable for the diagnosis because often this type of tumor does not readily shed cells during routine needle aspiration. A biopsy is often preferred as a first step for diagnosis of the mass.
Biopsy. A swelling that develops at the site of a previous vaccination or other injection should be considered malignant until proven otherwise. Such a swelling should be subjected to surgical biopsy and microscopic examination if the mass has been present for 3 or more months, if the mass is larger than 2 cm (just under one inch) in diameter or if the mass is increasing in size one month after injection.
Biopsy is a procedure in which a small portion of the mass is removed, preserved in a fixative solution, and sent to a laboratory for microscopic examination by a veterinary pathologist. Biopsy specimens can be obtained by an instrument called a Tru-Cut® needle (which collects a very small core of tissue) or by surgical incision of the mass to obtain a small wedge of tissue.
Radiographs. X-rays of the chest or nearby area of bone is often recommended to determine if any metastasis has occurred.
Because of the aggressive nature of the injection-site sarcoma, no single treatment has proved effective. However, treatment may include one or more of the following:
The most important thing you can do at home is to observe the area of concern carefully. Record when you first noticed the mass and seek advice from your veterinarian.
Regular visits to your veterinarian are critical to monitor your cat and treat this problem if it arises. Your veterinarian will examine the mass, measure and record its size and location, and discuss biopsy procedures with you.
After a veterinary pathologist has examined the biopsy specimen and given a diagnosis, appropriate treatment can be discussed and implemented by your veterinarian.
The only prevention is to eliminate vaccinations. However, since the incidence of injection-site sarcomas is low, it is wise to continue your immunization schedule. Consider vaccination every 3 years (rather than yearly) for rabies and panleukopenia. Limit vaccination for FeLV (feline leukemia virus) and FIP (feline infectious peritonitis) to at-risk cats as needed.
After immunizations, monitor your cat for swellings that may develop in body regions of previous injection or vaccination and see your veterinarian as soon as possible for early diagnosis and treatment.