The Journal of Clinical Oncology presents a Rapid Communications summary of the PENELOPE-B trial, a double-blind, placebo‐controlled, phase III study in women with HR+, HER2- primary breast cancer without a pathological complete response after taxane‐containing NACT and at high risk of relapse. With about one-third of women relapsing, palbociclib – a cyclin-dependent kinase 4 and 6 inhibitor – was examined.