John Bartlett, BSc, PhD, FRCPath, Ontario Institute for Cancer Research, Ontario, Canada, gives an overview of the Breast Cancer Index (BCI) prognostic model which can be used to predict the benefit from endocrine therapy for patients with HR+ breast cancer and late relapse. Data from the aTTom study (NCT00003678) of tamoxifen was used to train a cut point for the signature which could identify women who are at highest risk of late relapse and women at modest risk of late relapse. This interview took place at the virtual European Society for Medical Oncology (ESMO) Breast Cancer Congress 2021.