Objective: To compare results of treatment with temozolomide or dacarbazine, in combination with an anthracycline, in dogs with relapsed or refractory lymphoma.

Design: Nonrandomized, controlled clinical trial.

Animals: 63 dogs with relapsed or refractory lymphoma.

Procedures: Chemotherapy was administered in 21-day cycles. A combination of temozolomide and an anthracycline (doxorubicin or dactinomycin) was administered to 21 dogs and a combination of dacarbazine and an anthracycline was administered to 42 dogs. Efficacy and toxicoses were assessed.

Results: Thirteen of the 18 (72%) dogs treated with the temozolomide-anthracycline combination and 25 of the 35 (71%) dogs treated with the dacarbazine-anthracycline combination had a complete or partial response. Median duration of response to rescue chemotherapy was 40 days (range, 0 to 217 days) for dogs in the temozolomide group and 50 days (range, 0 to 587 days) for dogs in the dacarbazine group. The incidence of high-grade hematologic toxicoses was significantly higher among dogs in the dacarbazine group than among dogs in the temozolomide group, but the incidence of gastrointestinal tract toxicoses was not significantly different between groups. There were no significant differences between groups in regard to proportion of dogs with a complete or partial response, duration of response to rescue chemotherapy, survival time following rescue chemotherapy, or overall survival time.

Conclusions and Clinical Relevance: Both combinations had promise in the treatment of dogs with relapsed or refractory lymphoma, although administration of temozolomide was more convenient than administration of dacarbazine and caused fewer hematologic toxicoses.