Of 9366 patients enrolled in the parent ATAC trial, 1231 tumor samples from the two monotherapy arms were evaluable in the transATAC study, including 306 samples from patients with HR+, HER2-negative, N+ breast cancer (N = 243 with 1–3N+; N = 63 with ≥4N+). This evidence concerns the gene ERBB2 and breast cancer.