[Expression and promotor methylation of p73 gene in ovarian epithelial tumors].

OBJECTIVE: To investigate the expression and promoter methylation status of p73 gene in ovarian epithelial tumors and their clinicopathological correlations.

METHODS: Tissue microarrays (TMA) consisting of 68 ovarian cancers, 37 ovarian borderline tumors and 21 ovarian benign tumors were constructed. p73 expression was detected by immunohistochemistry (EnVision method). Fresh-frozen tissue samples from 13 cases of ovarian carcinomas and 5 cases of borderline tumors were evaluated for the presence of p73 promoter methylation using bisulfite sequencing.

RESULTS: Overall, 92.6% (63/68) ovarian carcinomas expressed p73, with a mean value of 32% (percentage of p73 positive cells in the tumor). The mean value of p73 expression rate (40%) in serous carcinoma (26/26) was higher than those of other cancer types (P = 0.006). The mean value of p73 expression rate (40%) in type II ovarian carcinoma was significantly higher than that in type I ovarian carcinoma (24%, P = 0.010). The expression of p73 was not associated with FIGO stage and histological grade (both P > 0.05). The mean values of p73 expression in ovarian borderline tumor (30/37) and benign tumor (12/21) were 16% and 15%, respectively. Of the two groups, the mean value of p73 expression rate in serous type was higher than that in mucous type (P = 0.003, P = 0.026). Ovarian carcinomas had a higher level of p73 expression than borderline tumors and benign tumors (both P < 0.05), while that between ovarian borderline tumors and benign tumors had no statistical difference (P > 0.05). Among serous tumors (49/53), the mean value of p73 expression in the carcinoma group (26/26) was significantly higher than those in the borderline tumor group (12/14) and benign tumor group (11/13; P = 0.024 and P = 0.002, respectively), while that between borderline tumor group and benign tumor group had no statistical difference (P = 0.428). Among mucous tumors (15/27), the mean value of p73 expression in carcinoma group (6/7) was higher than that in benign tumor group (1/8; P = 0.032). No statistical difference of p73 expression was seen between the carcinoma group and ovarian borderline tumor group (8/12) and between the borderline tumor group and benign tumor group (P = 0.234, P = 0.201, respectively). p73 promotor methylation was found in 8 of 13 cases of carcinomas but at different methylation levels with a mean value of 8.0%. Two of 5 ovarian borderline tumors showed detectable p73 promotor methylation with a mean value of 9.0%. Compared with the borderline tumors, ovarian carcinomas showed a similar p73 methylation level (P > 0.05). The p73 methylation level in ovarian carcinomas was not associated with histological type, pathogenetic type, histological grade and FIGO stage (all P > 0.05).

CONCLUSIONS: Most of ovarian epithelial tumors express p73 protein with mean values higher in ovarian carcinomas than those in the borderline and benign tumors. Ovarian serous carcinomas have the highest expression level of p73. A simple linear correlation does not exist between the promoter methylation and protein expression of p73.