ESR1 and breast cancer: There is contradicting evidence as to the effects of E2 on ER+ breast cancer cell invasion as some studies have shown that E2 reduces ER+ breast cancer cell invasion (Lymperatou et al., 2013), some show no effect (Thompson et al., 1988; Visser, 2013) and others, like our study, indicate an increase in ER+ breast cancer cell invasion (Thompson et al., 1988; Di et al., 2015).