Feline injection site sarcoma: immunohistochemical characteristics.

Objectives: Feline injection site sarcoma (FISS) is a rapid growing locally aggressive tumor with a low metastatic rate. Its histologic features are clearly defined, but there are few studies regarding its immunohistochemical characteristics. The present study investigated the immunohistochemical characteristics of 21 cases of FISS.
Methods: FISSs from 12 male and nine female cats, 20 mixed-breed and one Siamese, were included in the study. After histopathological diagnosis, additional histologic sections were immunostained for vimentin, cytokeratin, desmin, S100 protein, viral feline leukemia virus (FeLV) particles, cyclooxygenase 2 (COX-2) and c-KIT. Positive and negative controls were adopted accordingly. Immunostainings were classified as positive or negative according to the number of positive cells from a total of 1000 cells per tumor section.
Results: Histopathologic diagnosis of the tumors revealed 18 (85.7%) fibrosarcomas and three (14.3%) other sarcomas; four fibrosarcomas (22.2%) were grade III, five (27.8%) were grade II and nine (50.0%) were grade I. Two sarcomas were grade III and one was grade II. Seventeen (81%) tumors were negative for desmin. All samples were positive for vimentin. Twenty tumors (95.2%) were positive for S-100 protein. Positivity for c-KIT was observed in four (19%) samples; COX-2 was positive in 13 (61.9%) and FeLV viral particles were positive in nine (42.9%) FISSs.
Conclusions and Relevance: Immunohistochemical findings of FISSs revealed positive immunostainings for desmin, vimentin, S-100 protein, c-KIT, COX-2 and FeLV viral particles.