Response rate to a single dose of vinblastine administered to dogs with treatment-naive multicentric lymphoma.

Vincristine is included in vincristine, cyclophosphamide, doxorubicin and prednisone (CHOP) chemotherapy protocols, which are the gold-standard treatment for high-grade canine lymphoma. Vincristine can result in relatively high rates of gastrointestinal toxicity, whereas vinblastine is generally well tolerated and thus may represent an under-utilized and minimally toxic alternative to vincristine. Our objective was to determine the response rate and toxicity associated with a single dose of vinblastine administered to dogs with treatment-naïve, intermediate to large-cell, multicentric lymphoma. Twenty client-owned dogs were enrolled with signed owner consent. A Simon's minimax, phase II, two-stage trial was performed to test the efficacy of vinblastine administered at 2 mg/m2 IV followed by a pilot trial of vinblastine at 2.5 mg/m2 . No dogs were administered concurrent steroids or other chemotherapy. One out of 14 dogs receiving vinblastine at 2 mg/m2 demonstrated a partial response. Three out of five dogs demonstrated a partial response to vinblastine at 2.5 mg/m2 . Gastrointestinal toxicity was infrequent and low grade for both groups. The majority of dogs (80%) in the 2.5 mg/m2 dosing group developed neutropenia 1-week post administration. Vinblastine was well tolerated but minimally efficacious at a dose of 2 mg/m2 IV in dogs with treatment-naive, multicentric lymphoma. Because of poor response rates, treatment at this dose is not recommended. A small subset of dogs administered 2.5 mg/m2 had significantly improved response rates (P = 0.04), suggesting that higher doses may have improved efficacy, although further research is indicated to confirm these preliminary findings.