Up to 60% of endometrial cancer cases are attributed to obesity, in part because obesity promotes development of atypical endometrial hyperplasia (AEH), and up to 40% of women with AEH go on to develop endometrial cancer. The increasing prevalence of obesity in premenopausal women has resulted in increasing rates of AEH in this age group. Hysterectomy with removal of the fallopian tubes and ovaries is 100% effective in preventing endometrial cancer, but this approach results in infertility. Fertility-sparing treatments exist, such as treatment with oral or intrauterine progestin, but these treatments do not work uniformly and do not combat the underlying cause of endometrial cancer, which is obesity and metabolic syndrome. Additionally, up to 41% of women on progestin eventually experience relapse of AEH or endometrial cancer. Third, many patients have insulin resistance that may worsen with progestin therapy. Thus, to improve treatment of AEH and grade 1 endometrial cancer, prevent and reverse endometrial cancer, and allow women to preserve their fertility, the investigators must integrate an effective weight loss strategy to be given with progestin treatment. It is the hypothesis that premenopausal women with AEH desire uterine preservation will be more likely to have atypia-free uterine preservation at one year if they receive progestin in combination with a behavioral weight loss intervention versus progestin plus enhanced usual care.

Inclusion Criteria:

• Diagnosis of histologically confirmed complex atypical endometrial hyperplasia (AEH) or grade 1 endometrial cancer.

  • Patients with a previous diagnosis of AEH or grade 1 endometrial cancer who are already being followed with conservative management with oral or LNG-IUD progestin therapy are eligible.
  • For patients with a previous diagnosis of AEH or grade 1 endometrial cancer who have been placed on progestin prior to study entry, the duration of IUD or oral progestin use prior to trial entry should be documented.

• Premenopausal woman with a uterus.

• ECOG performance status of 0-2.

• At least 18 years of age and no more than 45 years of age.

• Undergoing uterine-sparing management (e.g. due to interest in fertility preservation, interest in uterine preservation, provider recommendation, or other reason).

• BMI ≥ 30 kg/m^2.

• Prior or current receipt of progestin is allowed as above. Willingness to undergo placement of LNG-IUD at the time of study entry.

• Ability to understand and willingness to sign an IRB approved written informed consent document.

Exclusion Criteria:

• Current, active treatment for any malignant neoplasm with chemotherapy or radiation.
• Pregnant and/or breastfeeding. Participants must have a negative urine or serum pregnancy test during screening window and within 7 days prior to LNG-IUD insertion. If LNG-IUD is in place, lack of pregnancy is assumed.
• Active pelvic infection at the time of IUD placement or other contraindication to the use of an IUD in the opinion of the treating physician.