BMP7 and breast cancer: However, it is possible that the increase in ActRII and ALK-2 gene expression and mRNA levels in the presence of estrogen observed in this study, was a counter mechanism to oppose the effects of estrogen, as a subsequent paper reported BMP-7 to also directly correlate with estrogen receptor (ER) expression changes (Schwalbe et al. 2003) in the context of estrogen-driven breast cancer.