GnRHa + Letrozole in Non-obese Progestin-insensitive Endometrial Cancer and Atypical Hyperplasia Patients

Inclusion Criteria: * Have a confirmed initial pathological diagnosis based upon hysteroscopy: histologically prove EAH or well-differentiated EEC G1 without myometrial invasion * BMI\<30kg/m2 * No signs of suspicious extrauterine involvement on enhanced magnetic resonance imaging (MRI) or enhanced computed tomography (CT) or ultrasound * Using progestin, any of the following therapy, as first-line treatment: 1. Megestrol acetate ≥ 160 mg qd using, combined with Levonorgestrel Lntrauterine System (LNG-IUS) inserted or not 2. Medroxyprogesterone acetate ≥ 250 mg qd using, combined with LNG-IUS inserted or not 3. LNG-IUS inserted * Progestin-insensitive: 1. remained with stable disease after 7 months of progestin use 2. did not achieve CR after 10 months of progestin use * Have a desire for remaining reproductive function or uterus * Good compliance with adjunctive treatment and follow-up Exclusion Criteria: * Combined with severe medical disease or severely impaired liver and kidney function * Pathologically confirmed as endometrial cancer with suspicious myometrial invasion or extrauterine metastasis * Patients with other types of endometrial cancer or other malignant tumors of the reproductive system * Patients with breast cancer or other hormone- dependent tumors or diseases that cannot be used with Diane-35, GnRHa, Letrozole or MET * Strong request for uterine removal or other conservative treatment * Known or suspected pregnancy * Acute severe disease such as stroke or heart infarction or a history of thrombosis disease * Smoker(\>15 cigarettes a day)