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)