Feline injection site sarcomas (FISSs) can be associated with vaccination sites as well as sites of other injection types (eg, antibiotics, long-acting corticosteroids, insulin). The reported incidence varies from 1.3/1,000–1/10,000 vaccinations. Risk factors include number of injections at a site and administration of cold versus room-temperature vaccines. Administration of 3–4 interscapular vaccines can double risk for sarcoma when compared with administering only 1 vaccination in that region. Sarcoma development is related to the presence of multiple growth factors, cytokines, and oncogenes.

Staging and treatment of FISSs involves imaging (eg, radiography, CT) for gross metastasis and/or the ability to achieve lateral surgical margins of 3–5 cm and 2 muscle layers deep. Outcome greatly depends on first surgery success. Patients often need 4–7 days of hospitalization for multimodal pain management. Heavy sedation is sometimes recommended for 24–48 hours postsurgery. Active suction drains and assisted feedings via esophagostomy tubes may assist recovery. Some specialists suggest following surgery with radiotherapy, but evidence of its benefits is inconsistent. Ongoing investigations include chemotherapy and immunomodulation.

Commentary
FISSs have changed vaccination practices and continue to challenge cautious practitioners to consider relative risk for a preventable disease, where on the body to administer vaccines, and how frequently we should vaccinate. We now must decide if more prudent vaccine protocols fit with both fiscal and practice standards. We should at least consider that vaccines be placed in separate locations on a cat’s body and emphasize the extremities for adjuvanted injections. Current recommendations suggest that no adjuvanted injection should be given in the scruff of the neck, the most difficult place to surgically remove a tumor.—Heather Troyer, DVM, DABVP, CVA

Source
Injection site-associated sarcoma in the cat: Treatment recommendations and results to date. Ladlow J. J FELINE MED SURG 15:409-418, 2013.