NCT03701334

Who might be able to join this trial:

• You have signed and dated a consent form before any trial-related tests begin.
• You are 18 years old or older when you sign the consent form.
• You are either male, or a female with a known menopausal status (either confirmed postmenopausal through surgery, age, hormone tests, or periods stopping for 12+ months, or confirmed premenopausal — all women who don't meet the postmenopausal criteria are considered premenopausal for this trial).
• You have been confirmed by biopsy or tissue sample to have a specific type of breast cancer (invasive adenocarcinoma) in one breast, and your diagnosis was made within the past 18 months.
• Your breast cancer tests positive for hormone receptors (estrogen receptor and/or progesterone receptor).
• Your breast cancer tests negative for the HER2 protein (confirmed by standard laboratory testing).
• You have stored tumour tissue available from your surgery that can be sent to a central lab (except for patients enrolling in China; and if you had treatment before surgery and the tumour disappeared completely, tissue from before that treatment is required).
• Your surgeon removed the tumour completely, with no cancer cells found at the edges of the removed tissue, and your cancer falls into a specific stage category (Stage III, Stage IIB, or certain Stage IIA cases — confirm exact stage eligibility with the trial site).
• If chemotherapy was recommended for you, you have already finished it before screening for this trial.
• If radiation therapy was recommended for you, you have already finished it before screening for this trial.
• There is no medical reason you cannot take the hormone therapy used in this trial, and you are planned to take it for at least 5 years.
• You may have already started standard hormone therapy, but you must join the trial (be randomised) within 12 months of first starting that therapy.
• You are generally well enough to carry out everyday activities with little or no limitation (as measured by a standard doctor's scale called ECOG Performance Status 0 or 1).
• Your blood counts, kidney function, liver function, and certain blood mineral levels (potassium, magnesium, calcium) are within acceptable ranges based on recent lab tests.
• Your heart's electrical activity, measured by a standard heart tracing (ECG), shows a normal heart rhythm (specific electrical interval below 450 milliseconds and resting heart rate between 50 and 90 beats per minute).
• You are willing and able to attend scheduled visits, follow the treatment plan, and complete all required tests and procedures.
• If you are a woman who could become pregnant, you have a confirmed negative pregnancy blood test within 14 days before joining the trial.
• If you are a woman who could become pregnant, you are willing to use a highly effective non-hormonal method of contraception during treatment and for 21 days after stopping treatment (acceptable methods include complete abstinence consistent with your usual lifestyle, surgical sterilisation, a vasectomised partner, or a copper intrauterine device — hormonal contraception is not allowed in this trial).

Who may not be able to join:

• You have previously received a type of cancer drug called a CDK4/6 inhibitor.
• You have used tamoxifen, raloxifene, or aromatase inhibitors (AIs) to reduce breast cancer risk or to treat osteoporosis within the past 2 years, or you are currently using hormone replacement therapy (HRT).
• You have previously received high cumulative doses of certain chemotherapy drugs called anthracyclines (above specific dose thresholds — confirm with trial site).
• You have a known allergy or sensitivity to the ingredients in the trial drugs, including certain rare sugar metabolism conditions or soy allergy (confirm with trial site).
• Your breast cancer has spread to distant parts of the body (stage IV), or there is evidence the cancer has come back after surgery.
• You are currently receiving any other cancer treatment, apart from the hormone therapy allowed in this trial.
• You have had major surgery, chemotherapy, or radiotherapy within the 14 days before joining the trial.
• You are still experiencing significant side effects from previous cancer treatments that have not sufficiently recovered (hair loss, certain nerve-related side effects, and some others may be exceptions — confirm with trial site).
• You currently have or recently had another invasive cancer, and its treatment finished within the past 2 years (certain treated