Clinicopathological features and outcome for dogs with mast cell tumors and bone marrow involvement

Background: Mast cell tumors (MCTs) with bone marrow (BM) involvement are poorly documented in dogs and are associated with a poor prognosis. Successful treatment strategies have not been described. Hypothesis: Clinicopathologic findings of affected dogs are not specific. Administration of lomustine or imatinib is beneficial. Animals: Fourteen dogs with MCT and BM involvement. Methods: Clinical and laboratory evaluations were performed in each dog on admission and during follow-up. All dogs received prednisone. Additionally, 8 dogs received lomustine and 3 dogs received imatinib. Imatinib was administered if tumorassociated tyrosine kinase KIT was aberrant. Results: On admission, 11 dogs had a single cutaneous nodule and 3 dogs had multiple nodules. Involvement of regional lymph nodes, liver, or spleen was observed in each dog. BM infiltration with mast cells (MCs) was observed in all dogs. On CBC, nonregenerative anemia, leukopenia, or thrombocytopenia was common. Four dogs had circulating MCs. Increased alkaline phosphatase or alanine transferase activity was observed in 12 and 10 dogs, respectively. Treatment with lomustine induced partial remission in 1 of 8 dogs. Median survival time was 43 days (range, 14–57). Dogs on imatinib experienced complete remission. Two dogs survived for 117 and 159 days, and the third was alive after 75 days. Dogs treated symptomatically did not improve and were euthanized after 1, 14, and 32 days. Conclusions and Clinical Importance: A combination of clinical and laboratory evaluation helps in identifying dogs with MCT andBMinfiltration. Administration of lomustine is not helpful in affected dogs. The beneficial effect of imatinib warrants further investigation.