Estimating the magnitude of clinical benefit from (neo)adjuvant chemotherapy in patients with ER-positive/HER2-negative breast cancer

Gene-expression assays were originally validated retrospectively as tools of prognostication, with evidence emerging from more recent prospectively-conducted studies such as MINDACT and TAILORx supporting their clinical validity and utility as biomarkers in identifying patients with luminal breast cancer who might be spared chemotherapy. However, these assays still do not have the ability to identify all patients who may safely avoid chemotherapy, and may over-estimate the risk of relapse in some cases. Future studies should aim to prospectively integrate contemporary approaches that assume a theoretical risk of relapse (based on pathological and/or genomic evaluation of the primary tumour), with new tools that can detect signals of active micro-metastatic disease. Until current methods of estimating prognosis and predicting benefit from adjuvant chemotherapy are significantly refined, estimating and improving the true magnitude of benefit derived from chemotherapy remains a challenge for clinicians.