MKI67 and breast cancer: When short courses of NET (2–4 weeks) are used, investigators have shown that changes in biomarkers such as the proliferation marker Ki67 can predict improved long-term outcomes and potentially guide adjuvant therapy decisions.3,4 The POETIC trial (perioperative endocrine therapy—individualizing care) is evaluating the relationship between change in Ki67 after 2 weeks of endocrine therapy and long-term outcomes in over 4000 post-menopausal women with HR-positive breast cancer with the goal of identifying patients who would benefit from additional adjuvant therapy.5–7