Abstract: Background – Chemotherapy for feline mammary carcinoma (fMC) is mostly doxorubicin-based in the literature. Vinorelbine, given in locally advanced and metastatic breast cancer in humans, demonstrated an acceptable toxicity profile in a previous phase I study in tumor-bearing cats. Hypothesis/Objectives – To evaluate the effectiveness and to characterize the toxicities of vinorelbine in fMC patients. Animals – Client-owned cats diagnosed with fMC and received vinorelbine at National Taiwan University Veterinary Hospital in 2017-2025. Methods – A single institutional retrospective study. Adverse events and response assessment were based on Veterinary Cooperative Oncology Group Common Terminology Criteria for Adverse Events (VCOG-CTCAE v2) and Response Evaluation Criteria for Solid Tumors in dogs (RECIST v1.0), respectively. Statistical analysis was performed to identify prognostic factors and clinical outcomes. Results – Twenty-three cats were included. All but one had previous surgery, and eleven (47.8%) had pulmonary metastasis before receiving vinorelbine. A total of 128 doses of vinorelbine were given; the median starting dose was 11.5 mg/m2 (range, 9-11.5), and a median of 6 doses were given per patient (range, 1-12). Two (2/11) had partial remission, and the overall response rate was 18%. Toxicities were self-limited: 19/23 (83%) had gastrointestinal toxicities (one grade 3), and 14/23 (61%) experienced neutropenia (7 were grade 3-4). Median progression-free survival was 95 days (95% CI: 50-158), and median overall survival was 310 days (95% CI: 140-431). Conclusions and Clinical Importance – Vinorelbine is a well-tolerated chemotherapy for fMC. A prospective, randomized, controlled study is warranted to further define its role in fMC.
