A Study to Learn More About How Well Elinzanetant Works and How Safe it is Compared to Placebo for the Treatment of Hot Flashes Caused by Anti-cancer Therapy in Women With, or at High Risk for Developing Hormone-receptor Positive Breast Cancer

Researchers are looking for a better way to treat women with, or at high risk for developing hormone-receptor positive breast cancer, who have vasomotor symptoms (VMS), a condition of having hot flashes caused by anti-cancer therapy. VMS, also called hot flashes, are very common medical problems in women with hormone-receptor (HR)-positive breast cancer, who are receiving anti-cancer therapy. HR-positive breast cancer is a type of breast cancer, which has hormone-receptors (proteins) for female sex hormones estrogen and/or progesterone. These hormone-receptors may attach to hormones like estrogen and progesterone and thereby help cancer cells to grow and to spread. Treatments that stop these hormones from attaching to these receptors are currently used to slow or stop the growth of HR-positive breast cancer. It is already known that women with HR-positive breast cancer benefit from this treatment. However, hot flashes are common medical problems related to this therapy. They negatively affect quality of life of many women and may lead to discontinuation (stopping) of this therapy. The study treatment, elinzanetant is being developed to treat hot flushes. It works by blocking a substance called neurokinin from sending signals to other parts of the body, which is thought to play a role in starting hot flashes. The main purpose of this study is to learn more about how well elinzanetant helps to treat hot flashes caused by anti-cancer therapy in women with or at high risk for developing HR-positive breast cancer compared to placebo. A placebo is a treatment that looks like a medicine but does not have any medicine in it. To answer this, the doctors will ask the participants to record information about their hot flashes before treatment start and at certain time points during the treatment in an electronic diary. The researchers will then assess possible average changes in number and severity of hot flashes after 4 and 12 weeks of treatment. To see how safe elinzanetant is compared to placebo. The study will collect information about the number of participants who have medical problems after taking treatment. The study participants will be randomly (by chance) assigned to 2 treatment groups, A and B. The participants from treatment group A will take elinzanetant. The participants from treatment group B will start with placebo and then switch to elinzanetant. All participants will continue taking the anti-cancer therapy they have been using when entering the study. Dependent on the treatment group, the participants will either take elinzanetant or placebo as capsules by mouth once a day. After 12 weeks, the participants who have initially received placebo will switch to take elinzanetant for the remaining 40 weeks. Each participant will be in the study for approximately 62 weeks. The treatment duration in the study will be 52 weeks. There will be up to 12 visits to the study site and 6 phone calls in between. Participants who completed the 52 weeks treatment phase, will be offered to continue treatment for another up to 3.5 years. During the study, the participants will: * record information about their hot flashes * answer questions about their quality of life and other symptoms. The doctors and their study team will: * check the participants health and vital signs * take blood and urine samples * examine heart health using electrocardiogram (ECG) * examine pelvic organs like womb or ovaries using a trans vaginal ultrasound scan to see images of these organs * make images of the breast using x-ray (mammogram), a type of radiation that passes through the body to make images of the inside and/or by using ultrasound (if applicable) * check the health of the participant's cervix (neck of the womb) by taking a small sample of cells (smear test) for an analysis called cervical cytology (if applicable) * take an endometrial biopsy, a small piece of tissue from the lining of the womb (called the endometrium) for analysis. * ask the participants questions about what medicines they are taking and if they are having adverse events. An adverse event is any medical problem that a participant has during a study. Doctors keep track of all adverse events that happen in studies, even if they do not think the adverse events might be related to the study treatments. About 4 weeks after the participants take their last treatment, the study doctors and their team will check the participants' health.