As this mechanism can be averted by focal hypofractionated RT delivered prior to P+T, a randomized, Phase II clinical trial (CIMER, NCT04563507) is currently recruiting subjects to investigate standard-of-care CDK4/6 inhibition plus ET vs SBRT followed by CDK4/6 inhibition plus ET in patients with oligometastatic (≤5 metastatic sites, no brain involvement) HR+HER2− breast cancer. The gene discussed is ERBB2; the disease is breast carcinoma.