High TM4SF1 expression was significantly associated with advanced histological grade, estrogen receptor negativity, and progesterone receptor status in primary tumors and with reduced relapse-free survival in estrogen receptor breast cancer patients when compared with ER+ patients, and this may be the reason that ER signaling inhibits TM4SF1 expression in breast cancer (Simpson et al., 2010). Here, ESR1 is linked to breast cancer.