Beyond 5 years: enduring risk of recurrence in oestrogen receptor-positive breast cancer

Women with early-stage oestrogen receptor (ER)-positive (ER⁺) breast cancer who receive standard endocrine therapy for 5 years remain at risk of distant recurrence for at least 15 years after treatment discontinuation. The extension of the duration of adjuvant endocrine therapy to 10 years has been shown to reduce the risk of recurrence only in a subset of women and, to date, predictive biomarkers of benefit from therapy do not exist. In this Review, we briefly explore the epidemiology of late recurrence (>5 years after diagnosis) in patients with ER⁺ breast cancer. The mechanisms underlying this phenomenon remain poorly understood; we discuss the evidence currently available on processes such as alterations of gene expression or specific genomic aberrations and examine several models used for risk prognostication and for estimating the presence of minimal residual disease, as well as the relevance of these prediction tools for clinicians and patients. Our aim is to enable clinicians to make well-informed decisions on whether to extend endocrine therapy for each individual patient.