Cancer Classification in Dogs

Recent veterinary studies have suggested that splenectomy should be a part of the treatment protocol for canine splenic lymphoma. The World Health Organization (WHO) lymphoma classification system has recently been applied to cases of canine lymphoma, and research suggests that canine splenic marginal zone lymphoma (MZL) may have a more indolent course of disease than other forms of lymphoma. The authors retrospectively reviewed outcomes of splenectomy for splenic lymphoma patients (n = 28). Results showed an overall 1-year survival of 59.8%, with patients with primary splenic lymphoma and no metastasis having better outcomes than those with distant metastases. For isolated B-cell splenic lymphoma, the 1-year survival rate was 69.8%; MZL and mantle cell lymphoma were the most common B-cell subtypes. Splenic T-cell lymphoma patients lived an average of only 5.7 days postoperatively. Patients with clinical signs such as weight loss or hemoabdomen had a poorer prognosis and were generally T-cell lymphoma patients. Prognosis was not predicted by any of the typical bloodwork parameters (eg, hematocrit, platelet count). Chemotherapy did not improve outcome in isolated splenic lymphoma in this study. The presence of splenic involvement in multicentric lymphoma is classified as Stage IV in the WHO system and in human medicine suggests a poor prognosis. The authors argue that while much of the WHO staging can be utilized in canine lymphoma, perhaps canine primary splenic lymphoma, with its indolent course, warrants a reappraisal of that classification in canines.

Cases in which dogs present with marked splenomegaly can be challenging. Hemangiosarcoma/hemangioma is often associated with focal or generalized splenomegaly, but this may also be seen in cases of splenic lymphoma. The latter may be nodular or infiltrative. Although cytology by ultrasound-guided fine-needle aspiration may help to obtain a diagnosis, the risk for rupture of the organ is high; spontaneous hemoabdomen may also occur. After a minimum preoperative work-up (ie, complete clinical examination, blood-

work, abdominal ultrasound, thoracic radiography), splenectomy should always be performed to obtain a definitive diagnosis and appropriate prognosis. In cases of splenic lymphoma, many dogs will achieve survival of >1 year, particularly those in which disease is found to be confined to the spleen only.—Paolo Buracco, DVM, DECVS