Chemoresistance Cytological Score for Canine Transmissible Venereal Tumour: A Proposed System of Predicting Vincristine Resistance

Canine transmissible venereal tumour (CTVT) is a common diagnosis in many low-income countries, and managing its chemoresistant cases can be challenging within the conventional vincristine sulfate chemotherapy protocol. Also, predictive markers of chemoresistance for this tumour remain unidentified. This study aimed to evaluate CTVT cytological characteristics to develop a predictive cytological scoring system for vincristine sulfate resistance. For this purpose, 40 cases were retrospectively analysed based on their clinical aspects and response to vincristine chemotherapy. First, cytological preparations underwent a double-blind assessment to evaluate a modified cytomorphological classification. This classification, an adaptation of a previously published system, categorised tumours based on cell shape (plasmacytic versus lymphocytic), but no association with chemoresistance was found (p = 0.083). Subsequently, a novel cytology scoring system was developed and tested to identify cases potentially associated with chemoresistance. This system was based on three criteria: anisokaryosis, mitotic count, and the presence of binucleated cells. Malignancy criteria, evaluated in 5 hotspots, were inversely associated with chemoresistance (p = 0.001), predicted by low anisokaryosis, a mitotic count of ≤ 6 in a 2.37 mm² area, and no binucleated cells. This study introduces a novel cytology scoring system for CTVTs, designed to serve as a predictive tool for vincristine treatment response. This system has the potential to aid practitioners in clinical decision-making. However, further studies are required to validate its reliability and applicability.