The primary objective is to compare the progression-free survival (PFS) between aromatase inhibitors interruption and aromatase inhibitors maintenance strategies in patients with a locally advanced or metastatic Low Grade Endometrial Stromal Sarcoma (LGESS).

Uterine sarcomas are rare tumors with an incidence of 1.7/100 000 women per year, including 20% of endometrial stromal sarcomas (ESS). Patients with low grade ESS (LGESS) have a good prognosis with a 5-year overall survival rates ranging from 66 to 98%, depending on the stage of the disease.

Majority of LGESS report estrogen receptor (ER) and/or progesterone receptor positive and a chromosomal translocation with JAZF1-SUZ12.

Based on the current European Society of Medical Oncology (ESMO)guidelines, the standard treatment for patients with early/non metastatic ESS is total hysterectomy plus or less bilateral salpingo-oophorectomy. The use of hormonal therapy (HT) for advanced or metastatic disease is recommended based on retrospective data from small series providing evidence that HT have an anti-tumor activity on LGESS. HT includes aromatase inhibitors (AI), progestins and gonadotrophin-releasing hormone.

Very few data are available in this rare disease, but retrospective analyses show that AI may provide response rates of 46 to 67% in metastatic LGESS patients (7% complete response, 60% partial response), with a mean duration of response of 24 months.

Even if AI are effective and well tolerated, chronical mild to moderate (grade 1-2) side-effects (arthritis, hot-flashes, osteoporosis, hypercholesterolemia, cardiac events) have a negative impact on patient's well-being because of the treatment long term duration and need to be balanced in such long term survival.

To date, the question of the optimal duration of HT in LGESS is still pending. The investigator propose an open-label, randomized, multicenter phase II study aiming at determining the feasibility of interruption of AI in patients with locally advanced or metastatic LGESS after long term stabilization or response to AI. The study will use a sequential bayesian design allowing for continuous monitoring of the main efficacy outcome, thus leading to a smaller more informative trial, and specifically tied to decision making. This design is particularly suited to characterize efficacy signals in the context of a very rare pathology. Moreover JAZF1-JJAZ1 fusion gene is not identified in all LGESS.

Ancillary studies will provide precious data aiming at:

• Identifying predictive factors of prolonged response to HT or late resistance (Next Generation Sequencing and Comparative Genome Hybridization).
• Evaluating sociobehavioral (only for French sites) of patients by following questionnaire: Zimbardo Time Perspective Inventory (ZTPI) , Functional, Communicative and Critical Health Literacy/ 14-item Health Literacy Scale (FCCHL/HLS14), VICAN, Fear of Cancer Recurrence (FCR) and Patient-Generated Index (PGI).

Inclusion Criteria:

• Age≥18 years;
• Histological confirmation of low grade ESS;
• Locally advanced or metastatic disease at diagnosis or patient experiencing a tumor effraction during hysterectomy;
• Treatment with aromatase inhibitors (Anastrozole or Exemestane or Letrozole ) initiated either: for at least 24 months (in patients with no residual disease or non-measurable disease at the last AI initiation) OR for at least 36 months (in patients with measurable disease at the last AI initiation);
• Disease must be controlled at the time of the randomisation (objective response or stable disease) by the aromatase inhibitor initiated either for at least 24 or 36 months
• Eastern Cooperative Oncology Group (ECOG) Performance Status (PS) ≤ 2
• Covered by a medical insurance;
• Signed informed consent prior to any study-specific procedure.

Exclusion Criteria:

• Pregnant or breastfeeding woman;
• Patient concurrently using other approved or investigational antineoplastic agents;
• Major concurrent disease affecting cardiovascular system, liver, kidneys, hematopoietic system or else considered as clinically important by the investigator and that could be incompatible with patient's participation in this trial or would likely interfere with study procedures or results;
• Prior history of malignancies other than study disease (except for basal cell or squamous cell carcinoma of the skin or carcinoma in situ of the cervix) unless the patient has been free of the disease for at least 3 years;
• Patients using prohibited concomitant and/or concurrent medications
• Contra-indication according to SmPCs.
• Patient requiring tutorship or curatorship.