Significance of p53 expression in background endometrium in endometrial carcinoma

The p53 signature (p53S) has been proposed to be a marker of the earliest phase of development of endometrial serous carcinoma. We examined the presence of p53S in the background endometrium in cases of endometrial carcinoma. From a series of 351 endometrial carcinomas, 225 (64.1 %) lesions, for which slides of the adjacent noncancerous endometrium were available for review, were included. Expression of estrogen receptor (ER)-alpha, Ki-67, and p53 in the adjacent endometrium was studied by immunohistochemistry. The p53S was defined as the presence of morphologically benign endometrial epithelial cells with moderate to strong intensity of p53 immunostaining. Of the 225 noncancerous endometrium samples, 34 consisted of hyperplastic and 191 of non-hyperplastic endometrium. A p53S was found in 22 cases (mean age 64.2 years), 2 in hyperplastic, and 20 in non-hyperplastic background endometrium. All p53S-positive cases also expressed ER-alpha; their median Ki-67 labeling index (LI) was 4.0 % (range 0.0 to 21.0 %). The two cases with hyperplastic p53S-positive background endometrium were in association with a grade 1 endometrioid tumor in a premenopausal woman with Lynch syndrome. Of the 152 cases of endometrioid adenocarcinomas with non-hyperplastic endometrium, 12 (8 %) were p53S positive, none of which associated with EIC. Of the 21 cases of serous carcinoma, five (24 %) were p53S positive, 4 of which (19 %) associated with EIC while in 5 others (24 %) EIC was found without p53S. Of three clear cell adenocarcinomas, none were p53S positive while two contained EIC without p53S. Of 15 carcinosarcomas, 3 (20 %) were p53S positive, all of which with EIC while 6 others (40 %) were associated with EIC but without p53S. Of the 8 non-endometrioid tumors with p53S, 7 (88 %) were associated with EIC. p53S is thought to be associated with precancerous lesions of non-endometrioid tumors, including carcinosarcomas.