Adverse Effects of Concurrent Carboplatin Chemotherapy and Radiation Therapy in Dogs

Background: Concurrent chemo‐ and radiotherapy improves outcome of certain human neoplasms but with increased signs of toxicity. Reports on adverse effects of concurrent chemo‐ and radiotherapy in the veterinary literature are scant. Objective: To report adverse hematologic and gastrointestinal effects of combined carboplatin and radiation therapy in dogs. Animals: Client‐owned dogs with spontaneously occurring neoplasia. Methods: Retrospective case study. Medical records of 65 dogs were reviewed. Criteria for inclusion were administration of radiation according to 1 of 3 fractionation schemes (19 × 3, 16 × 3, or 12 × 4 Gy) and administration of at least 1 concurrent carboplatin treatment at a dosage of 200–300 mg/m 2 . Dog and treatment‐related variables were analyzed for association with signs of intoxication. Results: Median carboplatin dosage was 200 mg/m 2 (range, 200–250 mg/m 2 ). Twelve of 58 dogs (21%) developed grade 3 or 4 neutropenia. Eleven of 56 dogs (20%) developed grade 3 or 4 thrombocytopenia. Six of 62 dogs (10%) developed grade 3, 4, or 5 gastrointestinal toxicosis. Analysis of association of dog and treatment‐related variables with signs of intoxication was hampered by the small numbers of dogs in individual groups, and no statistically significant associations were found. Conclusions and Clinical Importance: Combined modality therapy resulted in myelosuppression and gastrointestinal toxicosis. Future studies are needed to determine whether the potential benefit of combined modality therapy outweighs the risk of decreasing chemotherapy and radiation treatment intensity.