Proteomic characterization of ovarian cancers identifying annexin‐A4, phosphoserine aminotransferase, cellular retinoic acid‐binding protein 2, and serpin B5 as histology‐specific biomarkers

Numerous studies have suggested that the different histological subtypes of ovarian carcinoma (i.e. clear cell, endometrioid, mucinous, and serous) have distinct clinical histories and characteristics; however, most studies that have aimed to determine biomarker have not performed comprehensive analyses based on subtype specificity. In the present study, we performed two‐dimensional gel electrophoresis‐based differential proteomic analysis of the different histological subtypes of ovarian carcinoma using tissue specimens from 39 patients. Seventy‐seven protein spots (55 unique proteins) were found to be up‐ or downregulated in a subtype‐specific manner. The most significant difference was observed for: (i) annexin‐A4 (ANXA4) and phosphoserine aminotransferase (PSAT1), which are expressed strongly in clear cell carcinoma; (ii) cellular retinoic acid‐binding protein 2 (CRABP2), which is expressed specifically in serous carcinoma; and (iii) serpin B5 (SPB5), which is upregulated in mucinous carcinoma. Validation of these candidates by western blotting using a 34 additional test sample set resulted in an expression pattern that was consistent with the screening and revealed that differential expression was independent of cancer stage or tumor grade within each subtype. Thus, the present study reinforces the notion that ovarian cancer subtypes can be clearly delineated on a molecular basis into four histopathological groups, and we propose that ANXA4, PSAT1, CRABP2, and SPB5 are candidate subtype‐specific biomarkers that can help define the basis of tumor histology at a molecular level. (Cancer Sci 2012; 103: 747–755)