Feline mammary tumors: comparison of histological classifications and prognostic factors in a 3-year survival study (Part I)

Feline malignant mammary tumors are frequently aggressive and associated with poor clinical outcomes. Over the years, the prognostic value of various clinical and pathological parameters has been investigated, though findings are not always consensual. Histologically, feline malignant mammary tumors are heterogenous tumors, and a recent revision of the 1999 World Health Organization (WHO) classification of canine and feline mammary tumors may provide a more accurate picture of their biological behavior. This study aimed to analyze and compare the 1999 WHO classification and the 2019 updated surgical pathology classification in the same case series. Additionally, we seek to evaluate the prognostic value of several clinicopathological features, including both histological classification systems. Our findings revealed that the 2019 revised surgical pathology classification allowed for a greater stratification of feline mammary tumors (FMT) compared to the 1999 WHO classification system. Notably, longer survival times were observed in queens with ductal-associated carcinomas. Other clinicopathological features were associated with unfavorable clinical outcomes, namely presence of multiple synchronous malignant mammary tumors, larger tumor size, higher clinical stage, infiltrative tumor growth and lymphovascular invasion ( p ≤ 0.05). Additionally, our findings suggest that the prognostic relevance of each parameter may vary according to the clinical endpoint, warranting careful consideration during clinical interpretation. The data presented in this study are available from the corresponding author upon reasonable request. • The 2019 histological classification of feline mammary tumors provided a more refined stratification compared to the 1999 classification. • Ductal-associated carcinomas appeared to be linked to more favorable clinical outcomes than other malignant mammary tumor subtypes. • Clinical stage, type of tumor growth and lymphovascular invasion showed significant associations with overall survival, tumor-specific survival and disease-free interval. • The prognostic value of other clinicopathological features seemed to vary depending on the clinical endpoint.