Inclusion Criteria:

• Participants must be female and have Stage I, II, or III hormone receptor positive breast cancer based on clinical or pathologic evaluation.
• Participants must have been pre- or peri-menopausal at the time of breast cancer diagnosis by satisfying one of the following:
  • had a menstrual period (by self-report) within the 12 months before breast cancer diagnosis; or
  • had a serum or plasma estradiol and/or follicle stimulating hormone (FSH) concentration consistent with premenopausal status (based on institutional standards) within the 12 months before breast cancer diagnosis or when checked after breast cancer diagnosis.
• Participants must have started initial treatment with standard of care oral endocrine therapy (ET) (i.e., tamoxifen, anastrozole, exemestane, or letrozole; within 14 days prior to randomization or be planning to start initial treatment with standard of care oral ET within 14 days after randomization.
• Participants who currently have ovarian function (estradiol above the postmenopausal range) must be planning to undergo ovarian suppression or ablation concomitantly with oral ET medication, starting before or at the same time as oral ET initiation.
• Participants with chemotherapy-induced amenorrhea or ovarian failure at time of registration must be planning to start ovarian suppression or ablation if they have recurrence of ovarian function during study participation (circulating estradiol concentration in the premenopausal range or recurrence of menses).
• Participants must have completed surgery for treatment of breast cancer at least 14 days prior to randomization NOTE: Concomitant radiotherapy at the time of randomization and/or during study participation is allowed.
• Participants who received chemotherapy must have finished it at least 14 days prior to randomization.
  • NOTE: Concomitant maintenance targeted or biologic therapy (e.g., human epidermal growth factor receptor 2 [anti-HER2] therapy, poly-ADP ribose polymerase [PARP] inhibitor therapy, CDK4/6 inhibitor therapy, osteoclast inhibitor therapy) at the time of randomization and/or during study participation is allowed.
• Participants must be ≥ 18 years of age.
• Participants must have a complete medical history within 60 days prior to randomization.
• Participants must be able to complete Patient-Reported Outcome (PRO) instruments in English or Spanish.
• Participants must:
  • agree to complete PROs at all scheduled assessments; and
  • complete the pre-registration (baseline) PRO forms within 14 days prior to randomization.
• Participants must be able to complete symptom questions on a web browser (on a smartphone, tablet, or computer) or respond via voice on a telephone in English or Spanish. Participants must agree to complete symptom questions at all scheduled assessments.
  • NOTE: Participants who do not have access to the internet and who cannot receive telephone calls for interactive voice response system (IVRS) assessments are not eligible.
• Participants must be offered the opportunity to participate in specimen banking for translational medicine. With participant consent, specimens must be collected and submitted via the Southwest Oncology Group (SWOG). specimen tracking system.
• Participants must be informed of the investigational nature of this study and must sign and give informed consent in accordance with institutional and federal guidelines.

Exclusion Criteria:

• Participants must not have distant metastatic breast cancer.
• Participants who have started or plan to start treatment with tamoxifen during study participation must not have received prior tamoxifen for treatment or prevention of breast cancer.
• Participants who have started or plan to start treatment with an aromatase inhibitor during study participation must not have received prior aromatase inhibitor therapy for treatment or prevention of breast cancer.
• Participants must not be taking or planning to take oral estrogen-or progesterone-containing treatments during study participation.

NOTES: 

• Participants who start or plan to start treatment with an aromatase inhibitor may have previously received tamoxifen for prevention of breast cancer or treatment of a prior cancer.
• Participants may have received prior treatment with an aromatase inhibitor for infertility treatment.
• Participants must not be planning to become pregnant during the 80 weeks of study participation.
• Participants must not receive additional anti-cancer treatments (i.e., experimental therapy, immunotherapy, biologics, etc.) as part of another clinical trial.
• Participants must not have a non-breast malignancy for which they are currently receiving treatment.

Note: Other protocol defined Inclusion/Exclusion Criteria may apply.

Eligibility last updated 3/16/23. Questions regarding updates should be directed to the study team contact.