Serous versus high-grade endometrioid endometrial carcinoma: Immunohistochemistry of RFP is not useful for differentiation

We evaluated the immunohistochemical expression of ret finger protein (RFP) along with conventional immunohistochemical markers in endometrioid and serous carcinomas of the endometrium. A total of 124 endometrial carcinoma cases (24 grade 1 endometrioid, 60 grade 3 endometrioid, 40 serous) were retrieved from pathology archives. Tissue microarrays were constructed. The expression of RFP, WT1, ER, PR, p53 and p16 was examined im-munohistochemically. Sensitivity, specificity, area under the receiver operating characteristic (ROC) curve, ? statistic for interobserver reproducibility, Kruskal-Wallis test, Mann-Whitney U test and Fisher's exact tests were performed for statistical analyses. The mean RFP score was 1.54 in grade 1 endometrioid, 4.31 in grade 3 endometrioid, and 6.31 in serous carcinomas (p < 0.001). Overall, RFP scores were higher both in serous and grade 3 endometrioid carcinoma (p > 0.05), and significantly lower in grade 1 endometrioid carcinoma (p < 0.05). p16 and p53 staining patterns were able to differentiate between high-grade endometrioid and serous carcinoma (p < 0.001). ER, PR and WT-1 did not reach statistical significance for subtyping. The ? values of the general agreement between the observers were 0.737 and 0.727 for endometrioid and serous carcinomas respectively (p < 0.001). Diffuse p53 and p16 staining provides the most sensitive and specific immunomarkers for differentiating high-grade endometrioid and serous carcinomas.