Endometrial cancer is the fourth most common cancer among women, ranking after breast, lung, and colon cancer, and is the most common gynecologic cancer in the United States. According to Cancer Statistics for 2003, there were 40,100 estimated new cases of endometrial cancer in the United States and 6800 deaths attributable to this disease. The probability of endometrial cancer is highest at 60 to 79 years of age, when the relative risk reaches 1.59, compared with 0.73 from 40 to 59 years of age and 0.05 for age younger than 39 years. The overall 5-year survival rate for all women diagnosed with endometrial cancer from 1992 to 1998 was 86%, which has increased compared with the previous two decades. Most endometrial cancers are stage I (confined to the uterus) at diagnosis.According to the Surveillance, Epidemiology, and End Results (SEER) Program of the National Cancer Institute, localized disease represented 73% of all cases diagnosed from 1992 to 1999, regional disease represented 15% of cases, and distant disease represented only 8% of cases, with 4% of cases unstaged. In this survey, the overall survival rate for all stages of endometrial cancer diagnosed from 1992 to 1999 was 84%; for localized disease, it was 96%. The overall survival rate for regional disease was 65%; for distant disease, it was only 26%.The most common pathologic subtype is endometrioid adenocarcinoma, which arises from the endometrium and accounts for approximately 80% of malignant endometrial neoplasms. Aggressive variants of adenocarcinomas, including uterine serous and clear cell histologies, have a much poorer prognosis. Less common are uterine sarcomas, which arise from the myometrium or other mesenchymal elements of the uterine wall and account for only 2% to 5% of uterine malignancies. Of uterine sarcomas, carcinosarcoma (or mixed malignant mullerian tumors [MMMTs]) is the most common (8.2 per million women per year), followed by leiomyosarcoma (LMS; [6.4 per million]), both of which are somewhat more common in African American women than in white women. The incidence of MMMT increases with age, whereas the incidence of LMS peaks in middle age and then declines. The next most common type is endometrial stromal sarcoma (ESS; [1.8 per million]). The final group is known as unclassified (0.7 per million), and includes rhabdomyosarcoma, angiosarcoma, fibrosarcoma, chondrosarcoma, and liposarcoma.