Primary non-metastatic omental myofibrosarcoma in a horse

Myofibrosarcoma in horses is a rare malignant tumor composed predominantly by myofibroblasts. A 15-year-old horse was referred to the Veterinary Hospital of the Federal University of Parana for evaluation of colic signs. Initial physical examination showed icteric mucous membrane and laboratory analysis found anemia, increased serum activity of ALT, GGT, ALP, and bilirubin. In the exploratory laparotomy a highly vascularized abdominal mass in the left hypochondrium region of approximately 50cm x 45cm x 30cm, adhered to the surrounding structures was observed. Due to the size and adhesions to the omentum, the mass was considered surgically unresectable, and euthanasia was performed followed by necropsy. The immunohistochemical and morphological results indicate the diagnosis of myofibrosarcoma since the neoplastic cells immunoexpressed Vimentin, HHF35 and S100. To the authors' knowledge, this is the first equine case of omental myofibrosarcoma described in the literature.