The LUMINA trial is a prospective multicenter cohort study of patients ≥age 55 with grade 1–2, T1N0 breast cancer status, post-lumpectomy with ≥1 mm margins and luminal A subtype (ER ≥ 1%, PR >20%, HER2 negative and ki-67 ≤13.25%). This evidence concerns the gene ERBB2 and breast cancer.