Efficacy of vincristine as a rescue therapy for canine histiocytic sarcoma.

Canine histiocytic sarcoma (CHS) is a malignant tumor derived from macrophages and dendritic cells. Since effective chemotherapy is needed for CHS cases, we conducted this prospective study to evaluate the efficacy and adverse events of vincristine treatment as a rescue therapy for this disease. We administered vincristine to nine CHS cases that acquired resistance to lomustine or nimustine. Complete remission was achieved in one dog, partial remission in two dogs, stable disease in five dogs, and progressive disease in one dog. The median progression-free survival was 21 days (range: 7-71 days). Severe adverse effect was observed in one dog (Grade 3 thrombocytopenia). It is essential to establish novel effective treatments for CHS.