The study by Reyal et al., which used surrogate markers (ER- and HER2-receptor statuses) for molecular subtype assignment of a large series of > 2500 early-stage breast cancer patients treated with conservative surgery including an SLNB, found both ER-positivity and the interaction covariate between ER- and HER2-statuses to be significant predictors of a positive sentinel node (SN)8. The gene discussed is ESR1; the disease is breast cancer.