Vinorelbine as a Rescue Treatment for Canine Histiocytic Sarcoma: A Multicentre Retrospective Study of 18 Dogs

Histiocytic sarcoma (HS) is a highly metastatic cancer, and while response to several chemotherapy agents has been studied, the outcome remains poor. Vinorelbine (VNB) has been considered a possible treatment option, but data are limited. The aim of this study was to assess the efficacy and toxicity of VNB in canine HS. Medical records of dogs with HS, treated with VNB as first-line or rescue treatment, were reviewed. Overall response rate (ORR), progression-free survival (PFS), overall survival post-VNB (post.VNB.OST) and adverse events were evaluated. Associations between outcome measures and signalment, disease extent/location, diagnostic modality and response to previous chemotherapies were analysed. Eighteen dogs were included: 12 disseminated and six localised HS. VNB was a rescue treatment in all dogs. ORR was 38.9% [two complete responses (CR), five partial responses (PR)] including two dogs showing delayed best responses. Median PFS and post-VNB-OST for all dogs were 49 (95% CI: 33-166) and 75.5 days (95% CI: 55-174), respectively. Responders showed significantly longer median PFS (120 days) compared to non-responders (41 days). None of the other factors analysed were associated with ORR, PFS and post-VNB-OST, including pulmonary location. Neutropenia and gastrointestinal toxicity were common; however, the majority were low-grade with no hospitalisation required. Vinorelbine can be an effective and safe treatment for canine HS; disease location alone may not be a key predictive factor for VNB response and outcome. Further prospective studies on larger cohorts are required to confirm these findings.