Survival outcomes of dogs with multicentric lymphoma treated with sequential half-body radiotherapy and L-CHOP without maintenance chemotherapy

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BACKGROUND: L-CHOP (L-asparaginase, cyclophosphamide, doxorubicin, vincristine, prednisone) is the standard therapy for lymphoma in dogs, but relapse and limited long-term survival are common. Given the radiosensitivity of lymphoma, sequential half-body radiotherapy (HBRT) has been investigated to improve outcomes. HYPOTHESIS/OBJECTIVES: Evaluate progression-free survival (PFS), overall survival (OS), and adverse events in dogs treated with a no-maintenance L-CHOP protocol combined with low-dose-rate (LDR, 6 Gy; 8-14 cGy/min) HBRT compared to L-CHOP alone. ANIMALS: Client-owned dogs with intermediate- to high-grade multicentric lymphoma treated with L-CHOP-LDR-HBRT or a 6-month L-CHOP protocol (controls). METHODS: Medical records were retrospectively reviewed in this case-control study. Adverse events were graded using VCOG-CTCAE v2 (Veterinary Cooperative Oncology Group-Common Terminology Criteria for Adverse Events guidelines) criteria. RESULTS: Seventy-five dogs received L-CHOP-LDR-HBRT and were compared with 115 controls. Median PFS and OS for the L-CHOP-LDR-HBRT group were 532 days (95% confidence interval [CI], 389-782) and 752 days (95% CI, 526-963), significantly longer than in controls (296 days [95% CI, 260-331] and 457 days [95% CI, 382-553], respectively, P < .0001). A delay in irradiating the caudal half negatively affected PFS and OS. Adverse event data were available for 30 dogs treated with L-CHOP-LDR-HBRT; most were low-grade, with grade 3 and 4 toxicities occurring in 4.5% of all administered treatments. One dog required hospitalization after HBRT. Dose reductions and treatment delays were observed in 39 and 74 instances, respectively, over the 28-week protocol in this cohort. CONCLUSIONS AND CLINICAL IMPORTANCE: Combining L-CHOP with LDR-HBRT, without maintenance chemotherapy, might substantially extend PFS and OS over L-CHOP alone in dogs with multicentric lymphoma, with predominantly mild, manageable toxicities.

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