Winston, a 10 y/o DSH feline, was presented with a large palpable mass in the caudal right thigh. A needle biopsy was performed, identifying a post-vaccine giant cell fibrosarcoma. Vaccine-associated sarcomas have a range of presentations from relatively small freely moveable masses to large, firm, and fixed masses. The identification of the extent of disease through imaging of the tumor can potentially facilitate treatment planning. Contrast-enhanced computed tomography (CT) or magnetic resonance (MR) imaging is recommended to delineate the extent of disease. Tumor size based on external measurements and assessment provides only a suggestion as to the true extent of the local tumor. Tumor imaging also allows for a preliminary determination of the normal tissue structures that will be included in the surgical and/or radiation fields.

Winston’s mass extended from the mid femur distally to the level of the distal aspect of the tibial crest, and appeared to be situated between the biceps femoralis mm laterally and the gracilis mm medially. The popliteal lymph node was clearly visualized, and appeared to be incorporated into the distal aspects of the mass. Following a thorough discussion of the therapeutic options, these clients elected amputation. One month post operative follow up found Winston to be behaving normally, without any complications due to loss of limb.