Reproducibility for histologic parameters in peritoneal mesothelioma

Histologic subtype is recognized as a prognostic factor in malignant pleural mesothelioma. Specifically, epithelial morphology is associated with a better prognosis than other subtypes, and the same association is observed in peritoneal malignant mesothelioma. Recently, prognostic differences based on morphologic subtypes of epithelial peritoneal malignant mesothelioma were reported. Herein, we report the interobserver variability across four pathologists at three institutions. The authors independently reviewed 67 cases of malignant peritoneal epithelioid mesotheliomas and subclassified them according to their epithelial subtype: papillary, tubulopapillary, trabecular, micropapillary, solid and/or pleomorphic. The cases were also evaluated by each author for several other histopathologic parameters including depth of invasion, nuclear grade, lymphocytic host response, mitotic count/index, presence of lymphovascular invasion, and stromal desmoplasia. The interobserver agreement for histopathologic parameters was highest for mitotic rate (κ=0.36) and primary epithelial subtype (κ=0.32). The interobserver variability for solid subtype pattern was moderate (κ=0.49). We found that the interobserver variability for most histopathologic parameters is poor.