MammaPrint, a 70-gene expression assay that stratifies ER+ErbB2- breast cancers into low-risk (luminal A) and high-risk (luminal B), has been investigated in a phase III clinical trial (MINDACT TRIAL: NCT00433589), which showed promising results in selecting patients who can avoid adjuvant chemotherapy [9]. The gene discussed is ESR1; the disease is breast cancer.