Effect of repeated vincristine administration on platelet count in cats with lymphoma

Abstract Background Vincristine is a chemotherapy drug used to treat haemopoietic tumours such as lymphomas. In healthy dogs and those with immune‐mediated thrombocytopenia, vincristine administration increases platelet count. Conversely, myelosuppression is a reported adverse effect. However, information on the haematological effects of vincristine in cats is scarce. Therefore, this study aimed to determine platelet count variation following vincristine administration in cats with lymphoma. Methods A retrospective cohort study of cats receiving a cytological or histological diagnosis of lymphoma between 2010 and 2023 was conducted. Cats were eligible for inclusion if they received vincristine and a complete blood count was performed before and after its administration. Each vincristine administration was recorded as a sequential event. The change in platelet count following vincristine administration was then calculated. Results For the 52 cats included in the study, a total of 94 vincristine treatments were administered in up to four sequential treatment events. The cats' post‐treatment platelet counts were always higher than their pre‐treatment counts; however, the difference only became statistically significant after the second vincristine administration (mean difference 53.2 ± 124.4 × 10 3 µL; p  = 0.019). Limitations Due to the retrospective nature of the study, the blood sampling protocol was not standardised, and the timings of the complete blood count analyses differed between individual cases, which may have affected the results. Conclusion Repeated vincristine administration does not cause thrombocytopenia in cats with lymphoma and is not contraindicated in thrombocytopenic cats.