In order to evaluate adjunctive histologic methods for separating
mesothelioma (MM) and serous
adenocarcinoma (SC), we studied 28 and 46 respective cases histochemically and immunohistochemically. Ten serous
adenocarcinomas arose primarily in extraovarian sites within the abdomen. Diagnoses in each case were established retrospectively by a combination of electron microscopy and clinicopathologic correlation. A panel of
antibodies to
cytokeratin (CK),
epithelial membrane antigen (EMA),
B72.3,
placental alkaline phosphatase (PLAP),
S-100 protein,
carcinoembryonic antigen (CEA), Leu M1, CA-125, and
amylase (AM) was applied to
paraffin sections of each case. Serous
carcinoma was reactive for neutral
mucins whereas
mesothelioma was not; however, only 50% of
adenocarcinoma cases stained in this manner. Peritoneal
mesothelioma showed reactivity for CK (28 of 28 cases), EMA (24 of 28 cases), AM (five of 28 cases), CA-125 (four of 28 cases), and
S-100 protein (three of 28 cases), but lacked
B72.3, PLAP, and CEA. Three
mesotheliomas expressed Leu M1, but in an extremely focal distribution. Serous
carcinoma reacted for CK (46 of 46 cases), EMA (46 of 46 cases), CA-125 (42 of 46 cases),
S-100 protein (40 of 46 cases), Leu M1 (34 of 46 cases; with diffuse staining),
B72.3 (33 of 46 cases), PLAP (29 of 46 cases), AM (15 of 46 cases), and CEA (six of 46 cases). Two profiles (S-100 +
B72.3; S-100 + PLAP) were seen in 41 of 46 serous
adenocarcinoma cases but were absent in all
mesotheliomas. Hence, these combinations of determinants are effective in separating such
neoplasms diagnostically. Moreover, diffuse reactivity for Leu M1,
B72.3, PLAP, or CEA in papillary
peritoneal neoplasms appears to exclude the possibility of
mesothelioma; however, focal Leu M1 reactivity may indeed be seen in
mesothelioma. Although CA-125 is a sensitive marker for serous
carcinoma, it is not effective in distinguishing it from
mesothelioma.