The differences in immunohistochemical expression of p53, bcl-2, bax, estrogen receptor (ER), and progesterone receptor (PR) were evaluated in 40 endometrioid and 21 papillary serous carcinomas of endometrium and correlated with known predictors of survival, such as grade and stage. Uterine papillary serous adenocarcinomas (UPSA) showed significantly higher p53 expression than did uterine endometrioid adenocarcinomas (UEA) (76.2% versus 35%), whereas both ER and PR were more often positive in endometrioid than in serous tumors (p ؍ .005 and .0005). No significant difference was found in bcl-2 and bax expression between both histologic types. However, there was definite decrease in intensity of bcl-2 in UPSA compared with UEA. In endometrioid carcinoma, p53 overexpression was associated with high-grade and advanced-stage tumors (p ؍ .0006 and .006), whereas ER and PR expression was associated with low-grade and earlystage tumors (p ؍ .0006 and .0001; p ؍ .003 and .0006). Bcl-2 immunopositivity was more common in low-grade, early-stage rather than in high-grade, advanced-stage adenocarcinomas, but the difference was not statistically significant (p ؍ .24 and .07). Bax immunopositivity was associated with well-differentiated (p ؍ .04) and early-stage tumors. Furthermore, a significant inverse relationship between bax and p53 reactivity was defined (p ؍ .05), especially in tumors of endometrioid type. Bax and PR immunoexpression correlated near the limit of statistical significance (p ؍ .08), whereas no relationship was found among bax, bcl-2, and ER Endometrial adenocarcinoma (EA) is the most common gynecologic malignancy (1). Traditional factors associated with its prognosis include patient's age, tumor grade, stage, histologic type, and the depth of myometrial invasion. Two histologic types of EA-endometrioid and papillary serousare associated with different biologic behavior (2, 3). Uterine endometrioid adenocarcinomas (UEA) are usually accompanied by endometrial hyperplasia and typically are low grade, are early stage, and have favorable prognosis. Uterine papillary serous adenocarcinomas (UPSA) usually develop in an atrophic endometrium; are high grade; are advanced stage, and do not respond to conventional chemotherapy, radiotherapy, and hormone therapy (4, 5). Recently, a dualistic model of carcinogenesis has been proposed on the basis of the distinctive clinical and histologic features of endometrioid and serous adenocarcinoma (6). Based on this model, UEA is associated with a slow, estrogen-driven model of carcinogenesis whereby unopposed estrogen stimulation leads to the sequential malignant transformation through a stage of atypical endometrial hyperplasia. In contrast, a p53-driven model of