In addition, the specific biomarkers of ER+ subtype, ESR1 (Robinson et al., 2013; Spoerke et al., 2016), AGR3 (Garczyk et al., 2015), GATA3 (Ciocca et al., 2009), PCSK6 (Venables et al., 2008), BCAS1 (Fenne et al., 2013), PMAIP1 (Putnik et al., 2012), GPR77 (Zhu et al., 2021), and SCGB2A2 (Guan et al., 2003) have been demonstrated to be associated with breast cancer development or prognosis. Here, PCSK6 is linked to breast cancer.