Early results (at 5 years) of the single-arm IDEA study, in which post-operative radiotherapy was omitted for Oncotype Dx low-risk, ER-positive, HER2-negative breast cancer patients are encouraging, with low rates of ipsilateral breast recurrence (3.3% age 50–59, 3.6% age 60–69) reported at five years [84]. The gene discussed is ERBB2; the disease is breast cancer.