Clinical Utility of Patient-Derived Cell-Based In Vitro Drug Sensitivity Testing for Optimizing Adjuvant Therapy in Dogs with Solid Tumors: A Retrospective Study (2019–2023)

Inter-individual variations in drug responses are major concerns in cancer treatment in human and veterinary oncology. Consequently, preclinical models have been proposed to predict drug responses and determine optimal individualized therapy. We aimed to evaluate the clinical utility of in vitro drug sensitivity testing using a patient-derived cell culture model to select appropriate adjuvant therapies for dogs with solid tumors. We screened medical records of 126 dogs with suspected tumors, including 33 dogs with solid tumors (guided group, 16; empirical group, 17). Anticancer drugs used for adjuvant therapy were determined based on in vitro drug sensitivity testing (guided group) or histopathological examination (empirical group) results. Time to tumor progression (TTP) was compared between groups. The guided group had significantly longer TTP than the empirical group (949 vs. 109 days). Median TTPs were significantly longer in the guided group than in the empirical group for dogs with incomplete surgical margin (949 vs. 109 days), dogs with mitotic count < 20 per 10 high power fields (949 vs. 105 days), dogs with no evidence of metastatic disease at initial diagnosis (455 vs. 196 days), and dogs receiving tyrosine kinase inhibitors (949 vs. 109 days). Our study suggests that in vitro drug sensitivity testing may be a useful tool for optimizing adjuvant therapy in dogs with solid tumors.