Ribociclib And Endocrine Treatment of Physician's Choice for Locoregional Recurrent, Resected Hormone Receptor Positive HER2 Negative Breast Cancer

Collection of Correlative Samples at First Recurrence (Stage I consent) If feasible, optional correlative blood and fresh tissue will be collected during surgical excision of their 1st recurrence. Patients should then complete radiation therapy if that is indicated. Enrollment to the Treatment Phase will occur within 6 months of the last local treatment, surgery or radiation treatment, whichever occurred last. Study Treatment (Stage II/ main consent) Treatment includes: 1. Ribociclib: Oral ribociclib at a dose of 400 mg daily for 21 days out of a 28-day cycle. Ribociclib will be used in combination with ET per physician choice. 2. Physician's Choice Endocrine Therapy: ET consists of one of the following: * Intramuscular fulvestrant * Oral anastrozole * Oral letrozole * Oral exemestane * Concomitant use with tamoxifen is not allowed. Ribociclib administration is planned for 36 months and ET administration is planned for 60 months.