Dacarbazine as Single-Agent Therapy for Relapsed Lymphoma in Dogs

Background Multidrug resistance is the most common cause of treatment failure in dogs with multicentric lymphoma. 5-(3,3-Dimethyl-1-triazeno)-imidazole-4-carboxamide (DTIC) is an atypical alkylator used as standard treatment in human Hodgkin's lymphoma, and has been effective in combination treatment to treat resistant lymphoma in dogs. However, no data are available on the use of DTIC as a single agent in the treatment of relapsed canine lymphoma. Hypothesis Single-agent DTIC is effective and safe in treating dogs with lymphoma that relapsed or failed to respond to previous chemotherapy. Animals Forty client-owned dogs with relapsed lymphoma. Methods Dogs were eligible for the retrospective study if they had a histologically or cytologically confirmed diagnosis of lymphoma and had relapsed. Dogs received DTIC (800-1,000 mg/m2 every 2-3 weeks as a 4-5-hour IV infusion) and were evaluated for response rate and duration. Hematologic and gastrointestinal toxicity was assessed. Results The overall response rate for dogs being treated with DTIC was 35% (14 dogs) with a median progression-free interval of 43 days. Thirteen dogs had a partial response and 1 dog had a complete response. Stable disease was achieved in 3 dogs. Mild gastrointestinal toxicity was reported in 3 dogs posttreatment. Thrombocytopenia was the principal toxicity observed 7-14 days after the treatment. Treatments were delayed because of thrombocytopenia. Conclusions DTIC, when used alone, is effective in the treatment of dogs with relapsed lymphoma.