Histopathologic features predict survival in diffuse pleural malignant mesothelioma on pleural biopsies.

Malignant pleural mesothelioma is a rare tumor with a poor prognosis. The only universally recognized pathological prognostic factor is histopathological subtype with a shorter survival in non-epithelioid subtypes. Recently, a grading of epithelioid mesothelioma on surgical resection has been proposed. The aim of our work is to assess the prognostic role of several histopathological factors on a retrospective cohort of 116 patients diagnosed as a pleural mesothelioma for more than 95% of patients on pleural biopsy. Our work shows that mitotic count <3/10 HPF (p < 0.0001), the lack of necrosis (p = 0.0379), mild nuclear atypia (p = 0.0054), the lack of atypical mitoses (p = 0.0265), a nucleoli size <3 µm (p = 0.0139), and a nucleoli absent or visible at 200× or higher magnification (p = 0.0170) are significantly associated with a better median overall survival in epithelioid mesothelioma. The presence of atypical mitoses was found to be related to a worse median survival in non-epithelioid mesothelioma. Mitotic count, necrosis, nuclear atypia, and nucleoli size are not associated with overall survival in non-epithelioid mesothelioma. Our work highlights that histopathological prognostic factors can be assessed on pleural biopsies and can predict reliably median overall survival. This is of interest in order to define subgroups of patients who could benefit of different therapies and select patients who could benefit of surgical excision.