Significance of Fas receptor protein expression in epithelial ovarian cancer.

Fas receptor (FasR) is a cell surface receptor that, when activated, triggers apoptosis. It has been postulated that this receptor may be involved in the clearance of benign ovarian epithelial inclusion cysts (IC). In this study, we test the hypothesis that the expression of FasR changes among IC, cystadenoma (AD), tumors of low malignant potential (LMP), and invasive cancer (cystadenocarcinoma, CA). Formalin-fixed paraffin-embedded sections from 53 oophorectomy specimens representing 26 IC, 17 AD, 17 LMP, and 24 CA were stained using the immunohistochemical avidin-biotin-peroxidase method. We used a mouse antihuman monoclonal antibody Apo-1/Fas (Dako), at 1:5 dilution, after antigen retrieval. The stain was semiquantitatively scored by 3 observers evaluating the intensity of the stain and percentage of positive tumor cells. Statistical analysis was performed using the Wilcoxon rank sum test. Strong (score 6+/7+) and diffuse (>75%) luminal FasR stain was identified in 22 (85%) of 26 IC and 16 (94%) of 17 AD, but only in 6 (35%) of 17 LMP and 1 (4%) of 24 CA. Conversely, weak (score 2+/3+) and focal (<25%) FasR staining was observed in 7 (29%) of 24 CA, but in none of the IC, AD, or LMP. These differences were statistically significant (P < .05). The decreased expression of FasR in malignant ovarian epithelial neoplasms as compared with benign ovarian epithelial lesions suggests that a decreased sensitivity to Fas-mediated apoptosis may be involved in ovarian epithelial carcinogenesis.