This observation in two independent data sets is consistent with the notion that a high grade ER- and HER2-negative sub-cluster might comprise primarily of samples with low aggressiveness as previous reports show that PDGFR expression is rather associated with high histopathological grade in ER-negative, HER2-positive breast cancer samples (Carvalho et al., 2005; Paulsson et al., 2009; Ahmad et al., 2011) and that INSR up-regulation is imminent in approximately 90% of breast cancer samples with bad prognosis (Nielsen et al., 2004; Law et al., 2008). Here, ESR1 is linked to breast cancer.