ESR1 and breast cancer: The SPECTRUM (Substitution of Paclitaxel for Cyclophosphamide on Survival Outcomes and Resumption of Menses in Young Women with ER [Estrogen Receptor]–Positive Breast Cancer) trial20 was designed to compare the survival outcomes of standard adjuvant epirubicin plus cyclophosphamide followed by weekly paclitaxel (EC-wP) and epirubicin plus paclitaxel followed by weekly paclitaxel (EP-wP) in young women with breast cancer.