Trial Parameters
Brief Summary
This research study is looking to see how well male breast cancer responds to preoperative treatment with endocrine therapy and which endocrine therapy regimen is the most effective treatment for male breast cancer. The drugs used in this study are: * Tamoxifen * Anastrozole * Degarelix * Abemaciclib
Eligibility Criteria
Inclusion Criteria: * Men aged 18 years or older, with diagnosis of invasive breast cancer who have not undergone surgical resection of the primary tumor and axillary nodes. * Stage I, II, or III per American Joint Committee on Cancer (AJCC) staging 8th edition (112). * Breast cancer must be hormone receptor-positive and HER2-negative according to definition below assessed by local pathology. * Hormone receptor-positive is defined as: positivity for at least one of the hormone receptors (estrogen receptor \[ER\] or progesterone receptor \[PR\]) by IHC. ER and PR assays are considered positive if there are \> 1% positive tumor nuclei in the samples. * HER2-negative is defined per the current American Society of Clinical Oncology/College of American Pathologists Clinical Practice Guideline (113). * Patients with multifocal or multicentric disease are eligible if the treating investigator has determined the patient should be treated as ER-positive and HER2-negative. * Bilateral breast can