Prognosis associated with equine lymphoma is often grave, and treatment is often non-curative. Few studies have evaluated long-term outcome following chemotherapy in horses treated for lymphoma. The purpose of this study was to report long-term outcome of horses with lymphoma treated with chemotherapeutic protocols. Eleven horses were included following medical record search and case recruitment via the ACVIM LAIM and Oncology Diplomate listserves. Eight horses had multicentric lymphoma and three horses had cutaneous lymphoma. T-cell rich large B-cell lymphoma was the most common immunohistochemical classification (n = 6). Three horses were EHV-5 positive on biopsy samples of neoplastic tissue. Chemotherapeutic agents included cyclophosphamide (n = 9), vincristine (n = 9), lomustine (n = 8), L-asparaginase (n = 7), doxorubicin (n = 6), cytosine arabinoside (n = 2), chlorambucil (n = 1), and intra-lesional cisplatin (n = 1). Adjunctive treatments included corticosteroids (n = 9) and valacyclovir (n = 3). Complete remission was achieved in 5 horses (45.5%), partial response was achieved in 3 horses (27.3%), stable disease was achieved in 1 horse, and 2 horses died during treatment. Overall response rate was 73% (8/11). All 3 horses with EHV-5 associated lymphoma achieved complete remission. Two pregnant mares were treated, with one mare surviving to foaling. Overall median survival time was 13 months (range, 1 - 41 months). Median survival time for multicentric lymphoma (n = 8) was 7.5 months (range, 1 - 28 months) and median survival time for cutaneous lymphoma (n = 3) was 21 months (range, 16 - 41 months). Seven of 11 horses exhibited a total of 11 adverse effects directly attributed to chemotherapy. Adverse effects were graded according to the VCOG-CTCAE grading system (grade 1 alopecia, n = 2; grade 1 combined neutropenia and lymphopenia, n = 2; grade 1 lymphopenia, n = 1; grade 1 lethargy, n = 1; grade 2 gastrointestinal signs, n = 1; grade 2 injection site reaction, n = 1; grade 2 hypersensitivity, n = 1; grade 4 hypersensitivity, n = 1; grade 5 hypersensitivity, n = 1). Higher grade adverse effects were most commonly associated with doxorubicin administration (n = 3), including one horse that died 18 hours post-administration. This report is limited by its retrospective nature, particularly the variation in treatment. However, these findings show that chemotherapy can be used successfully for treatment of equine lymphoma. Adverse effects, most commonly mild, occurred in approximately two-thirds of treated cases.
Resident, Large Animal Internal Medicine
University of Pennsylvania School of Veterinary Medicine New Bolton Center
Thursday, June 14
11:45 AM – 12:00 PM
Thursday, June 14
12:00 PM – 12:15 PM
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