MKI67 and breast cancer: A retrospective series of 686 ER+/HER2− BC were reclassified using AJCC 2018, and in the group of 521 patients for which AJCC 2018 recommends molecular evaluation, we assessed the prognostic efficacy of a prognostic stage enriched by Ki67 (Ki67-PS), considering Ki67 <20% an alternative to recurrence score <11 provided by Oncotype DX.