Director Signature Animal Medical Center Seoul, Seoul-t'ukpyolsi, Republic of Korea
Abstract: Background - Vincristine and cyclophosphamide are core agents in canine lymphoma protocols. While generally tolerated, small breed dogs may exhibit higher toxicity, making it crucial to evaluate the impact of cumulative exposure on treatment continuity. Hypothesis/Objectives - To evaluate the distribution of adverse effects (AEs), their correlation with chemotherapy delays, and the impact of cumulative treatment cycles in small breed dogs weighing under 15 kg. Animals - Twenty-one client-owned small breed dogs weighing under 15 kg (median: 5.4 kg) diagnosed with lymphoma.Methods - Multi-center retrospective study reviewing records from Jeju National University (Jan 2021 – Oct 2024) and Signature Animal Medical Center (Jan 2025 – Dec 2025). A total of 72 vincristine and 35 cyclophosphamide administrations were analyzed. Maximum AE grade was defined as the highest VCOG-CTCAE v2 grade recorded for each dog. AEs were assessed both per administration and across cumulative treatment cycles. Results - AEs occurred in 81.3 % of dogs during the study period. Chemotherapy delays were significantly frequent when total AE scores exceeded 3 for vincristine (P = 0.0003) and 2 for cyclophosphamide (P = 0.0287). Cumulative exposure (> 5 or > 9 doses) did not significantly correlate with grade > 2 AEs. Conclusions and Clinical Importance - The 81.3 % AE incidence is notably higher than previously reported in studies with larger median body weights, suggesting very small dogs face higher toxicity risks. Total AE scores better predict delays than individual grades, emphasizing the need for composite monitoring in extremely small breed dogs.
