Thymoma diagnosis and categorization in the current scenario: Morphological analysis based on interobserver variability

BACKGROUND: Thymomas are not so common tumors that are encountered in day-to-day pathology reporting. The WHO system was proposed in 2015. Although, through its detailed reporting, the WHO elaborates all subtypes and morphological clinches to diagnosis, it was important to ascertain its reproducibility in our day-to-day reporting. AIMS: The aims of the study were (1) to study the interobserver agreement, concordance rates, and variability in the classification of a large number of thymomas received in our department as per the WHO 2015, (2) to correlate the WHO subtype with Masaoka–Koga stage, and (3) to study the variations in demography of thymomas in Indian patients as compared to those reported in the literature. SETTING AND DESIGN: This retrospective study was done at a tertiary care teaching hospital with huge surgical oncology patient load, also pertaining to the cardiothoracic surgeries. It is predominantly an interobserver agreement design to study the reproducibility of the WHO 2015 classification on thymic epithelial tumors. METHODS: Four pathologists have independently reviewed histopathology slides of 65 cases of thymomas and classified them into predefined categories. Kappa statistics was applied to the observations. RESULTS: There was a substantial interobserver agreement in overall classification of thymomas with a Cohen's kappa score of 0.66. A better score was achieved for the classification of Group B thymomas. The WHO subtypes correlate well with the Masaoka–Koga staging system, and this finding is statistically significant. This article also presents the clinical details of a large number of thymoma cases. CONCLUSION: The new WHO classification has good reproducibility among pathologists in thymoma reporting.