EVALUATION OF SINGLE-AGENT MITOXANTRONE AS CHEMOTHERAPY FOR RELAPSINGCANINE LYMPHOMA

Many chemotherapeutic regimens will induce remission in dogs with lymp homa, but almost all dogs suffer relapse. Mitoxantrone was selected fo r evaluation as single-agent chemotherapy for relapsing canine lymphom a based on its use in humans undergoing salvage chemotherapy for non-H odgkin's lymphoma and its tumoricidal effect against canine lymphoma. Dogs entered into study had multicentric lymphoma, and all had been tr eated solely with a standard combination chemotherapy protocol. At Ist relapse, all dogs were again staged and underwent lymph node biopsy. Mitoxantrone was administered IV at 6 mg/m(2) every 21 days. Dogs were evaluated for lymphadenopathy before each dose of mitoxantrone. Fifte en dogs were entered into study. The average age (+/-SEM) of the dogs studied was 7.7 +/- 0.91 years, and most dogs were large (mean +/- SEM weight, 24.44 +/- 2.15 kg). Twelve dogs (80%) had B-cell lymphoma, an d 3 had T-cell lymphoma. Dogs were staged IV (n = 12) or V (n = 3). Th e median duration of chemotherapy before entry into the study was 98 d ays. Overall median duration of response after mitoxantrone chemothera py was 21 days. Complete responses were attained in 7 of 15 dogs (47%) with a median response duration of 84 days. Nine of 15 (60%) dogs att ained a complete remission with additional chemotherapy after failing mitoxantrone chemotherapy. Mild toxicities were observed after mitoxan trone administration. No adverse reactions were observed during mitoxa ntrone infusions. The results of this study demonstrate that mitoxantr one, as a single agent, has limited value for dogs with lymphoma at Is t relapse after conventional multidrug chemotherapy.