Retrospective evaluation of clinical outcome after chemotherapy for lymphoma in 15 equids (1991‐2017)

Background Prognosis associated with lymphoma in horses is poorly characterized, and treatment is often palliative. Long‐term outcome after chemotherapy for horses with lymphoma is not well documented. Objective To report long‐term outcome of horses with lymphoma treated with chemotherapy. Animals Fifteen equids. Methods Retrospective case series. Medical record search and call for cases on the ACVIM listserv for horses treated with chemotherapy for lymphoma. Results Fifteen cases with adequate data were identified. Complete remission was achieved in 5 horses (33.3%), partial response was achieved in 9 equids (60%), and stable disease was achieved in 1 horse. Overall response rate was 93.3% (14/15). Overall median survival time was 8 months (range, 1‐46 months). Nine horses experienced a total of 14 adverse effects attributable to chemotherapy. Adverse effects were graded according to the Veterinary Cooperative Oncology Group common terminology criteria for adverse events grading system (grade 1 alopecia, n = 2; grade 1 neutropenia, n = 2; grade 1 lymphopenia, n = 3; grade 1 lethargy, n = 1; grade 2 neurotoxicity, n = 1; grade 2 colic, n = 1; grade 1 hypersensitivity, n = 1; grade 2 hypersensitivity, n = 2; grade 5 hypersensitivity, n = 1). Higher grade adverse effects most commonly were associated with doxorubicin administration (n = 4), including 1 horse that died 18 hours post‐administration. Conclusions and Clinical Importance Chemotherapy can be used successfully for treatment of horses with lymphoma. Adverse effects, most commonly mild, occurred in approximately two‐thirds of treated horses.