Long‐term remission and survival in dogs with high‐grade, B cell lymphoma treated with chemotherapy with or without sequential low‐dose rate half‐body irradiation

Abstract Background Standard of care for dogs with high‐grade lymphoma, multiagent chemotherapy, achieves good initial responses but long‐term remissions are infrequent; previous studies using half‐body irradiation suggest improved long‐term outcomes. Hypothesis The addition of low‐dose rate half‐body irradiation would improve outcomes in dogs with B‐cell lymphoma. Animals Client‐owned dogs with stage III or higher, substage a, B‐cell lymphoma that achieved complete remission after 4 doses of multiagent chemotherapy. Methods A case‐controlled design comparing 2‐year remission and survival rates between dogs treated with CHOP‐based chemotherapy and those treated with chemotherapy and sequential low‐dose rate half‐body irradiation. Results Thirty‐eight dogs were enrolled with 18 included in final analysis, 9 prospectively‐enrolled dogs and 9 case‐matched historical controls. The irradiation cohort's 2‐year disease‐free rate was 56% whereas median duration exceeded the 730‐day study period compared with 0% and 261 days in the chemotherapy only group. Remission duration significantly differed between cohorts (P < .01), hazard ratio 0.218 (95% CI: 0.06‐0.77). The irradiation cohort's 2‐year survival rate was 78% with median overall survival duration exceeding the 730 day study period compared with 11% and 286 days in the chemotherapy only group. Overall survival time significantly differed between cohorts (P < .02), hazard ratio 0.173 (95% CI: 0.03‐0.839). Conclusions and Clinical Importance The improved long‐term outcome achieved by dogs administered sequential low‐dose rate half‐body irradiation in this study is similar to previous observational studies. Where long‐term remission is sought in dogs with B‐cell lymphoma low‐dose rate half‐body irradiation could be considered in addition to standard chemotherapy