Stephen Shaw, DVM, DACVIM (Oncology) Veterinary Medical Specialists (Campbell)

howtoissInjection site sarcomas can be frustrating tumors to effectively treat. These tumors are extremely infiltrative in nature; therefore, treatment recommendations for them commonly include multiple modes of therapy. Excision with wide surgical margins in conjunction with pre-operative or post-operative radiation therapy is the recommended course of treatment, and provides the longest disease free interval. Conservative excision is associated with a median tumor free interval of 2 months, while more aggressive surgeries are associated with a median tumor free interval of 9 months. The combination of radiation therapy and surgery is associated with median disease free intervals of 13-20 months. Ideally, we would love to see the patients before surgery is performed to help with the pre-operative decisions. Our ability to safely and effectively use radiation is dependent on the decision making that occurs prior to surgery.

Historically, the interscapular location of injection site sarcomas made it difficult to treat them and difficult to differentiate which injections were responsible for them. Vaccination recommendations written by the Vaccine Associated Sarcoma Task Force in1996 were published to try to address these problems. The recommendations stated that rabies vaccines should be administered in the right rear limb, FeLV vaccines in the left rear limb, and FVRCP vaccines in the right shoulder; all were to be administered as distally as possible. The last–and arguably most important–part of the recommendation to administer each injection as distally as possible is often overlooked or forgotten. When vaccines or injections are administered in proximal limbs, the resultant tumors that form usually extend onto the abdominal wall or around the pelvis, making surgical excision difficult–even with amputation of the associated leg. In these instances, wide surgical excision would mean resecting body wall or performing hemipelvectomies in addition to radiation therapy. By administering injections more distally in a limb, any subsequent tumors in these in these locations can be potentially cured by amputation and there is a reduced need for adjuvant radiation therapy.

After publication of the Vaccine Associated Sarcoma Task Force vaccination guidelines (www. avma.org/vafstf/sitercmnd.asp), there was a decrease in the incidence of interscapular tumors and an increase in caudal body tumors, including those that occur on the flank and abdominal wall. In a recent study, such tumors were presumed to have formed in these locations due to a cat’s tendency to crouch down with their pelvic limbs tucked up under their abdomen. With their abundant loose skin, an injection intended for the subcutaneous space over their thigh could easily be misplaced into skin that stretches over the flank or caudal abdomen when the cat stands and extends its legs.

Treatment for ISS in cats begins even before the tumor develops. As this is an iatrogenic disease, those who provide vaccinations and injections to cats can help facilitate treatment of this aggressive tumor by adhering to the Vaccine Associated Sarcoma Task Force’s vaccination recommendations. Management of cats that are suspected to have ISS may be optimized by consulting with an oncologist prior to initiation of surgical treatment.