Testing Whether Hormone Therapy With Ribociclib is as Effective as Chemotherapy Followed by Hormone Therapy With Ribociclib for the Treatment of High Anatomic Stage Breast Cancer With Low Recurrence Risk, The RxFINE-Low Trial

Inclusion Criteria: * STEP 0: Patient must be ≥ 18 years of age * STEP 0: Patient must have an Eastern Cooperative Oncology Group (ECOG) performance status of 0-2 within 28 days prior to Step 0 pre-registration * STEP 0: Patient must be a postmenopausal woman or a man * NOTE: Menopause can be determined by any of the following: * Prior bilateral oophorectomy * Age ≥ 60 years * Age \< 60 years with amenorrhea for ≥ 12 months and estradiol and follicle stimulating hormone (FSH) levels in the postmenopausal range * NOTE: FSH and estradiol levels should be repeated as clinically indicated to ensure menopausal status in patients with breast cancer with chemotherapy-induced amenorrhea * STEP 0: Patient must meet one of the following staging criteria postoperatively according to American Joint Committee on Cancer (AJCC) 8th edition criteria * pT0-T3 with 3 positive ipsilateral lymph nodes (micro-or macrometastatic disease) and no planned axillary lymph node dissection after definitive surgery in the breast and axilla with curative intent. * pT0-T3 with N2 or N3 * pT3 with N0-N3 * NOTES: * Patients with T4 breast cancer are not eligible. * Positive isolated tumor cells (ITCs) in axillary nodes without micro- or macrometastasis are considered N0 for eligibility purposes. * ITC does not contribute to nodal count for staging purposes * STEP 0: Patient must have a primary breast tumor that is estrogen receptor (ER) positive with \> 10% ER…