Researchers are looking for a better way to treat women with nonatypical endometrial hyperplasia (NAEH).

Endometrial hyperplasia is a condition where the lining of the uterus (called the endometrium) becomes too thick. Nonatypical means that the condition is not cancerous. It is often caused by hormone imbalances in women. Symptoms can include abnormal vaginal bleeding or irregular periods. If this condition is not treated, then it may lead to cancer.

Currently, there are no approved treatments for NAEH and that is why there is still an unmet medical need.

The study treatment, Mirena (also known as BAY 865028), is already available as a type of birth control device. It is inserted into the uterus where it gradually releases progesterone.

In this study, researchers want to find out if Mirena works for women with NAEH. They believe it can help by keeping hormone levels balanced in the body.

The main purpose of this study is to show that uterine lining goes back to completely normal lining after treatment with Mirena and that its use is safe in this population.

For this, the researchers will compare the number of participants with benign endometrium after 6 months of treatment with Mirena or oral MPA.

The study participants will be randomly assigned into one of two treatment groups. The randomization will be done 2:1 ratio, meaning that for every two participants assigned to Mirena, one will be assigned to oral medroxyprogesterone acetate (MPA). Based on their group, participants will receive Mirena, which is inserted into the uterus at the start of the study, or they will take progestins once daily by mouth for 6 months.

Each participant will be in the study for around 10 months with up to 5 visits to the study clinic/site.

Participants will visit the study clinic:

• once before the treatment starts
• 3 times with a gap of 3 months between the visits during the treatment
• then 1 more time after the treatment ends

During the study, the doctors and their study team will:

• check participant's health by performing tests such as blood and urine tests
• perform vaginal ultrasound and hysteroscopy. Hysteroscopy is a minor surgical procedure where a thin camera will be inserted into the womb to check for any abnormality. Sampling of the endometrial lining (cells in the womb) will be done with a thin tube at the same time.
• take samples of womb (endometrial) lining
• ask the participants questions about how they are feeling and what adverse events they are having

An adverse event is any medical problem that a participant has during a study. Doctors keep track of all adverse events, irrespective if they think it is related or not to the study treatment.

Inclusion Criteria:

• Post-menarchal women (≥18 years) at the time of signing the informed consent.
• Women with histologically confirmed NAEH independent of their parity or menopausal status. Endometrial samples will be obtained either at screening or no more than 42 days prior to the signing of the informed consent form.

Exclusion Criteria:

• Any diseases or conditions that might interfere with the conduct of the study or the interpretation of the results.
• Congenital or acquired uterine or cervical anomaly including fibroids, or cervical stenosis that in the opinion of the investigator, would interfere with insertion and/or retention of the intrauterine system (i.e., if they distort the uterine cavity).
• Use of any long-acting injectable sex-hormone preparations within 6 months prior to the start of study intervention, and /or short acting hormonal medication within 6 weeks prior to the start of study intervention.
• Pregnancy
• Participants with either known family or personal history of genetic predisposition to uterine, ovarian or colorectal cancers (e.g. Lynch syndrome).

The study population will be nulliparous and parous women (≥18 years of age) independent of their menopausal status.

Availability of this study's data will later be determined according to Bayer's commitment to the EFPIA/PhRMA "Principles for responsible clinical trial data sharing". This pertains to scope, timepoint and process of data access. As such, Bayer commits to sharing upon request from qualified researchers patient-level clinical trial data, study-level clinical trial data, and protocols from clinical trials in patients for medicines and indications approved in the US and EU as necessary for conducting legitimate research. This applies to data on new medicines and indications that have been approved by the EU and US regulatory agencies on or after January 01, 2014. Interested researchers can use www.vivli.org to request access to anonymized patient-level data and supporting documents from clinical studies to conduct research. Information on the Bayer criteria for listing studies and other relevant information is provided in the member section of the portal.