This concept will be tested further in early-stage breast cancer in the ongoing eMonarcHER trial: a randomized, double blind, placebo-controlled phase III trial (N = 2450) of abemaciclib plus standard adjuvant endocrine therapy in participants with high-risk, node-positive, HR+/HER2+ early breast cancer who have completed adjuvant HER2-targeted therapy (NCT047523320). The gene discussed is ERBB2; the disease is breast cancer.