Phase 2 Randomized Trial to Examine Ovarian Function Suppression for Breast Cancer (OFS)

Inclusion Criteria: * Female subject aged ≥ 18 years * Pre- or peri-menopausal patient, who had (1) menses within the 12 months prior to enrollment or (2) estradiol concentration above the postmenopausal range per institutional laboratory guidance within the 12 months prior to enrollment * Planning to take GnRHa therapy in combination with oral endocrine therapy (tamoxifen, anastrozole, exemestane, or letrozole) for adjuvant treatment of stage 1-3 breast cancer or for treatment of metastatic breast cancer * Not planning bilateral salpingo-oophorectomy during the 6-month study duration * Completion of chemotherapy, if given. Concurrent use of trastuzumab, pertuzumab, bisphosphonate therapy, poly adenosine diphosphate-ribose polymerase (PARP) inhibitor therapy, cyclin D kinase 4/6 (CDK4/6) inhibitor, and/or phosphoinositide 3-kinase (PI3K) inhibitor therapy is permitted * Able to provide informed consent and willing to sign an approved consent form that conforms to federal and institutional guidelines Exclusion Criteria: * Prior bilateral salpingo-oophorectomy * Known to be pregnant or breastfeeding (negative pregnancy test will be confirmed prior to study treatment initiation) * Concomitant use of systemic or transdermal estrogen products * Known allergy or hypersensitivity to goserelin or leuprolide, or any of the excipients in the medications * Unable to take oral medications * Any medical condition that would interfere with the absorption of endocrine therapy. Prior gastric bypass is permitted * Patients with a prior or concurrent malignancy whose natural history or treatment, in the opinion of the treating investigator, has the potential to interfere with the safety or efficacy assessment of the investigational regimen