STANDARDIZATION INITIATIVE FOR CANINE MAMMARY TUMOURS: NATIONAL GUIDELINES, MULTI-INSTITUTIONAL RING TEST AND DIAGNOSTIC ALGORITHM

Introduction: Standardization of histological diagnosis is a matter of debate both in human and veterinary medicine, particularly for heterogeneous lesions such as canine mammary tumours (CMTs). Classification of CMTs has evolved over time; however, the accuracy of histological diagnosis is inadequately understood and often includes misleading terminology and variable/personal interpretation resulting in non-uniform diagnosis and impossibility to compare studies and interchange data. As an initiative of the Italian Association of Veterinary Pathology (AIPVET), a panel of 15 veterinary pathologists was formed with the aim to i) discuss the last Davis-Thompson DVM Foundation CMTs classification and develop guidelines for its application, ii) quantify interobserver diagnostic agreement, and iii) develop a graphic diagnostic algorithm. Materials and methods: The panel performed 25 meetings, identified critical points of CMT classification and agreed on consensus guidelines, arranged a blinded ring test on 36 CMTs and discussed the structure of a diagnostic algorithm. Results: Critical points were discussed and precise guidelines were elaborated including a consensus on robust prognostic markers and content of the histopathological report. Overall concordance rate (kappa analysis) of diagnostic interpretations showed substantial and moderate agreement, respectively, for identification of hyperplasia-dysplasia vs benign vs malignant lesions and morphological diagnosis of histotype. A diagnostic algorithm was produced to be tested for efficacy in further studies. Conclusions: Consensus guidelines can help standardization, producing moderate to substantial agreement; however, additional efforts such as development of easy to apply algorithms are needed to further reduce interobserver variability in CMT classification.