Ovarian atypical proliferative (borderline) mucinous tumors: gastrointestinal and seromucinous (endocervical-like) types are immunophenotypically distinctive.

Ovarian atypical proliferative (borderline) mucinous tumors of gastrointestinal and seromucinous types are considered subtypes within the mucinous tumor category despite the presence of distinctive clinicopathologic features that seromucinous tumors share with pure serous tumors. Immunophenotypic differences have not been extensively investigated. Immunohistochemical studies were performed to compare the expression patterns of cytokeratins 7 and 20 (CK7, CK 20), estrogen and progesterone receptors (ER, PR), CA-125, mesothelin, and WT-1 in 28 tumors of gastrointestinal type and 12 tumors of seromucinous type. Both gastrointestinal and seromucinous type tumors had a high frequency of CK7 expression (93% and 100%, respectively). The gastrointestinal type tumors were characterized by frequent expression of CK20 (86%) and CDX2 (39%), infrequent expression of CA-125 (11%) and mesothelin (7%), and lack of expression of ER, PR, and WT-1. In contrast, the seromucinous type tumors were characterized by frequent expression of ER (100%), PR (67%), CA-125 (92%), and mesothelin (83%), infrequent expression of WT-1 (8%), and lack of expression of CK20 and CDX2. The gastrointestinal and seromucinous types of atypical proliferative mucinous tumors are immunophenotypically distinctive tumors. The former are characterized by expression of markers of gastrointestinal-type differentiation (CK20 and CDX2), whereas the latter are characterized by expression of "müllerian-type" markers (ER, PR, CA-125, and mesothelin). Expression of the latter markers in the seromucinous tumors, which also are expressed in pure serous tumors, and lack of expression of gastrointestinal-type markers, combined with the clinicopathologic features these tumors share with pure serous tumors, support the concept that this subtype is more closely related to serous than gastrointestinal type mucinous tumors and justify the designation "seromucinous."