Some cases of endometrial cancer are dependent on estrogen for their growth. Letrozole blocks estrogen production in the body. The purpose of this study is to determine if the investigators can predict which patients might benefit from Letrozole treatment by studying the many different forms of the estrogen receptor molecule that exist within the cancer tissues. To participate in this study, the patients must be 40 years of age or older and have biopsy-proven endometrial carcinoma, either well differentiated or moderately differentiated forms. Also, to be eligible to participate in this study, the patients need to be healthy enough to have a hysterectomy. If the patients are less than age 60, they will need a blood test (FSH) to confirm that they have gone into menopause.

Inclusion Criteria:

• FIGO grade 1 or 2 endometrioid adenocarcinoma of the endometrium
• Post menopausal status must be demonstrated
• Signed informed consent

Exclusion Criteria:

• FIGO grade 3 endometrioid adenocarcinoma or non-endometrioid cancers of the endometrium
• Younger than 40 or postmenopausal status not established
• Pregnant or breastfeeding

Subjects and controls selected to give groups similar in age and tumor grade. Four subjects excluded - wrong tumor type. One treatment arm completed but was excluded from analysis because of late completion.

Weekly by telephone interview during treatment

Adverse events for control arm not collected.