Histiocytic sarcoma in a one-year-old springer spaniel

A one-year-old female Springer Spaniel was presented with a firm mass in the left submandibular region and fixed palpable infraorbital masses. On cytological examination of the submandibular mass, a diagnosis of lymphoblastic lymphosarcoma was proposed. Radiographs revealed multiple pulmonary nodules and a suspicious lytic lesion in the right scapula. Histopathology revealed a pleomorphic arrangement of large round cells with a high mitotic index and high nuclear to cytoplasmic ratios, resembling a malignant histiocytic population. Immunohistochemistry on lung masses at necropsy was inconclusive but consistent with a highly anaplastic malignant neoplasm. Based on the clinical, morphological and histopathological findings, histiocytic sarcoma was diagnosed. Histiocytic sarcoma is extremely rare in dogs of such a young age. No other cases of histiocytic sarcoma in a dog this young were found in an extensive literature review of the subject.