A 48-year-old premenopausal woman presents with a mammogram-detected right breast invasive ductal carcinoma (IDC), grade II, positive for both estrogen and progesterone receptors (ER and PR) and HER2-negative. Ki-67 is 15%. She undergoes a partial mastectomy and sentinel lymph node biopsy (SLNB), with pathology showing a 2.1-cm tumor, no lymphovascular invasion, negative margins, and 1 out of 2 SLNs positive for metastasis. Complete blood count and comprehensive metabolic panel are unremarkable.