Efficacy of dacarbazine as a rescue agent for histiocytic sarcoma in dogs.

Background: Canine histiocytic sarcoma (HS) is an aggressive neoplasm that is generally associated with a poor prognosis. CCNU is considered first-line medical therapy, although the majority of dogs ultimately develop progressive disease. The objective of this study was to evaluate the efficacy of dacarbazine as a rescue agent for HS.

Methods: Medical records of dogs diagnosed with HS that received at least one dose of dacarbazine were reviewed. Information collected and analyzed included signalment, disease distribution, treatment history, dacarbazine treatments (including dose, interval and total number of cycles), adverse events, and response to treatment.

Results: Seventeen dogs were included, all of which had disseminated or metastatic disease and had received prior treatment with CCNU. Three dogs achieved partial remission for an overall response rate of 17.6%. The overall median event-free survival (EFS) was 21 days. For dogs that experienced an objective response, the EFS was 70 days. Toxicity secondary to dacarbazine was generally mild and self-limiting.

Conclusions: In the setting of advanced disease, dacarbazine appears to have modest activity against HS and warrants further investigation.