Recognition and reporting of histologic features in canine integumentary mast cell tumors: An assessment of interpathologist agreement

Canine integumentary mast cell tumors (CIMCTs) are common, and their clinical behavior can vary significantly. In an attempt to predict their biological behavior, veterinary pathologists utilize grading systems and assess specific histologic features, which are thought to carry prognostic significance. Assessment of interpathologist agreement with CIMCT grading systems has been investigated. However, for most individual histologic features that form the basis of these grading systems, there has been no investigation into how consistently they can be recognized and reported. This study evaluated the interpathologist agreement for morphologic diagnosis (ie, cutaneous vs subcutaneous mast cell tumors) and 31 histologic features commonly evaluated in CIMCTs by developing 2 surveys, without (survey 1) and with (survey 2) written definitions. Twenty-three veterinary anatomic pathologists located in 8 countries completed the surveys, which included 20 CIMCTs. Interpathologist agreement was calculated for each feature using Krippendorff's alpha values (α). The degree of agreement for morphologic diagnosis was moderate (α = 0.452) and substantial (α = 0.611) in surveys 1 and 2, respectively. In both surveys, there was suboptimal (α < 0.400) agreement among pathologists in evaluating most histologic features (21/31 in survey 1; 20/31 in survey 2). Ulceration, tumor depth and width, and deep histologic tumor-free distance had the best agreement (range = 0.597-0.929) in both surveys. The features with the worst agreement (α ≤ 0.100) in both surveys were cytoplasmic granularity, degree of demarcation, degree of infiltration, chromatin pattern, nucleolar number, and nucleolar prominence. Written definitions did not categorically change interpathologist agreement for most (24/31) histologic features.