Drapkin et al., (2005) observed that HE4 was not expressed in mucinous ovarian cancer and normal ovarian tissues; however, it was expressed in 50% of the ovarian clear cell carcinomas, 93% of the serous ovarian cancers and 100% of endometroid carcinomas of the ovary. This evidence concerns the gene WFDC2 and ovarian serous adenocarcinoma.