Mediastinal histiocytic sarcoma with abdominal metastasis in a Somali cat

A nine–year-old female neutered Somali cat presented with a one-month history of weight loss and inappetance. Thoracic radiographs revealed an extensive cranial mediastinal mass, and fine needle aspirate cytology and core needle biopsies were initially suggestive of a thymoma. The mass was excised via a mid-ine sternotomy and partial pericardectomy. Clinical signs recurred four weeks postsurgery and investigations revealed recurrence of a mediastinal mass, pleural effusion and an additional small mass cranial to the right kidney. Histopathological examination and immunohistochemistry of the previously resected mass prompted a revised diagnosis of histiocytic sarcoma (HS) with abdominal metastasis. The cat was treated with doxorubicin and lomustine but did not respond well and was euthanased two months later. HS is an uncommon neoplasm in cats with only two cases of mediastinal involvement reported in the literature. This case underlines the importance of immunohistochemistry in the evaluation of mediastinal masses.