38 © 2009 The Authors. Journal compilation © 2009 Blackwell Publishing Ltd Original Article DOI: 10.1111/j.1476-5829.2008.00170.x Keywords canine, chemotherapy, lymphosarcoma, rescue Correspondence address: Nicole Northrup Department of Small Animal Medicine and Surgery University of Georgia College of Veterinary Medicine Athens GA 30602 USA e-mail: northrup@uga.edu Introduction MOPP (mechlorethamine [Mustargen; Ovation Pharmaceuticals, Deerfield, IL, USA], vincristine [Vincristine; Mayne Pharma (USA), Paramus, NJ, USA], procarbazine [Matulane; Sigma-Tau, Gaithersburg, MD, USA] and prednisone [Prednisone; Roxane Laboratories, Columbus, OH, USA]) (Table 1) is an effective rescue protocol for canine lymphoma. 1 A retrospective study of 117 dogs treated with MOPP for resistant lymphoma reported a complete remission rate of 31% for a median duration of 63 days and a partial remission rate of 34% for a median duration of 47 days. 1 The MOPP protocol was generally well tolerated; however, 28% of dogs experienced gastrointestinal side- effects. These adverse effects were severe enough to require hospitalization in 13% of treated dogs, and three dogs were killed because of severe gastroen- teritis. Additionally, five dogs developed febrile neutropenia and three of these dogs died. Overall, 5% of treated dogs died as a result of toxicity. Because the majority of dogs treated with MOPP have failed protocols that include vincristine and because mechlorethamine and procarbazine are not known to modulate mechanisms of resis- tance to vincristine (VCR), 2 we hypothesized that removal of VCR from the protocol would not affect response rates or progression free survival. In addi- tion, because the dose-limiting toxicity of a single *Present address: Department of Veterinary Clinical Sciences, Louisiana State University, Skip Bertman Drive, Baton Rouge, LA 70803, USA. † Present address: Upstate Veterinary Specialists, 393 Woods Lake Road, Greenville, SC 29607, USA. ‡ Present address: Department of Biomedical Sciences, Cornell University, Ithaca, NY 14853, USA. § Present address: Purdue University, College of Veterinary Medicine, 625 Harrison Street, West Lafayette, IN 47907, USA. Mechlorethamine, procarbazine and prednisone for the treatment of resistant lymphoma in dogs N. C. Northrup 1 , T. L. Gieger 1 *, C. E. Kosarek 1 , C. F. Saba 1 , B. E. LeRoy 2 , T. M. Wall 1† , K. R. Hume 1‡ , M. O. Childress 1§ and D. A. Keys 1 1 Comparative Oncology Program, Department of Small Animal Medicine and Surgery, University of Georgia, College of Veterinary Medicine, Athens, GA, USA 2 Comparative Oncology Program, Department of Pathology, University of Georgia, College of Veterinary Medicine, Athens, GA, USA Abstract Forty-one dogs with resistant lymphoma were treated with a modified MOPP (mechlorethamine, vincristine, procarbazine and prednisone) protocol (MPP [mechlorethamine, procarbazine and prednisone] administered on a 21-day cycle, shortened from the 28-day MOPP cycle). The overall response rate to MPP was 34% for a median of 56 days (95% confidence interval 30–238). Seventeen percent of dogs had a complete response for a median duration of 238 days, 17% had a partial response for a median of 56 days and 32% had stable disease for a median of 24 days. Histological grade or cell morphology on cytology was associated with response. Minimal toxicity was observed with the MPP protocol, suggesting that further dose intensification or addition of another chemotherapeutic agent would be possible.