There is great appreciation for the heterogeneity of breast cancers, particularly of hormone-receptor positive breast cancers. A goal of modern oncology managing such heterogeneity is to determine how to individualize therapy based on the specific pathological and biological features of a given tumor. Two distinctive clinical literatures exist to guide treatment of hormone-receptor-positive breast cancer. The Oxford Overview, a seminal meta-analysis effort, has recently been updated, and suggests that nearly all patients with ER-positive tumors benefit from adjuvant endocrine therapy. In addition, the overview finds that nearly all subsets of patients with ER-positive tumors also benefit from modern adjuvant chemotherapy regimens. Meanwhile, retrospective subset analyses of specific trials or populations suggests that the benefits of chemotherapy are not so uniform, and in particular that molecular diagnostics assays can identify patients who do not warrant chemotherapy. This article will highlight recent data and controversies in personalizing adjuvant breast cancer therapy.