Management of Atypical Endometrial Hyperplasia and Endometrial Carcinoma Using Megestrol Acetate

Inclusion Criteria: * Women with a diagnosis of atypical endometrial hyperplasia or G1 or G2 endometrial carcinoma confirmed by an New York University (NYU) pathologist desiring medical management will be eligible. The diagnosis may be obtained either by endometrial biopsy or D\&C. If diagnosis has been made outside of NYU, slides must be available for review. * Age \> = 18 years. * Life expectancy of greater than 12 months. * Gynecologic Oncology Group (GOG) performance status score of 0, 1 or 2 * Patients must have normal organ and marrow function as defined below: * leukocytes \> = 3,000/mcL * platelets \> = 100,000/mcL * total bilirubin within normal institutional limits * AST(SGOT)/ALT(SGPT) no greater than 2.5 X institutional upper limit of Normal * glucose \< 200 mg/dl * creatinine within normal institutional limits OR * creatinine clearance \> = 60 mL/min/1.73 m2 for patients with creatinine levels above institutional normal * Eligibility of patients receiving any medications or substances known to affect or with the potential to affect the activity or pharmacokinetics of Megace will be determined following review of their case by the Principal Investigator. * The effects of Megace on the developing human fetus at the recommended therapeutic dose are unknown. For this reason and because Megace is known to be teratogenic, women of child-bearing potential and men must agree to use adequate contraception (hormonal or barrier method of birth control; abstinence) prior to study entry and for the duration of study participation. Should a woman become pregnant or suspect she is pregnant while participating in this study, she should inform her treating physician immediately. * Ability to understand and the willingness to sign a written informed consent document. Exclusion Criteria: * Patients with a histological diagnosis of clear cell, papillary serous or poorly differentiated (G3) endometrial carcinoma. * Patients with cancer have an MRI showing evidence of extrauterine spread or myometrial invasion. * Presence of US findings suspicious for ovarian malignancy, unclear endometrial primary or recurrent endometrial cancer. * Patients receiving other investigational agents. * Patients with a history of a previous thrombotic event, known thrombophilic condition or poorly controlled diabetes. * Patients with a history of breast cancer or other hormonally responsive malignancy. * Uncontrolled intercurrent illness including, but not limited to, ongoing or active infection, symptomatic congestive heart failure, unstable angina pectoris, cardiac arrhythmia, or psychiatric illness/social situations that would limit compliance with study requirements. * Pregnant women are excluded from this study because Megace has the potential for teratogenic or abortifacient effects. Because there is an unknown but potential risk for adverse events in nursing infants secondary to treatment of the mother with Megace, breastfeeding should be discontinued if the mother is treated with Megace.