Table 4 Proposed guidelines for the diagnosis of Localized Malignant Mesothelioma^a

Imaging studies: well circumscribed serosal/subserosal mass of any size

Absence of additional nodules or other evidence of diffuse serosal spread in the pleura, pericardium or peritoneum

Presence of serosal effusion (e.g., pleural effusion, ascites, pericardial effusion) does not exclude the diagnosis if cytology is negative for malignant cells (see below)

Presence of pleural, pericardial or peritoneal thickening adjacent to the tumor raises questions about the diagnosis; malignancy needs to be excluded by biopsy of any serosal abnormality other than the localized mass

Thoracoscopy or laparoscopy: absence of additional tumor nodules;

Biopsy all pleural abnormalities

Biopsies of grossly normal serosa away from the tumor are not required for diagnosis

Cytology: absence of malignant cells in effusion, preferably confirmed by loss of BAP-1

immunoreactivity in the malignant cells (benign mesothelial cells retain BAP-1

immunoreactivity) and/or CDKN2A p16 loss of heterozygosity in atypical mesothelial cells

Histopathology: presence of histopathologic features and immunophenotype that are identical to those of diffuse malignant mesothelioma