 Additionally, high levels of CSF-1 expression are observed in the endometrial epithelium of the pregnant uterus as well as high levels of its receptor CSF1R in the placental trophoblast.Studies have shown that activation of trophoblastic CSF1R by local high levels of CSF-1 is essential for normal embryonic implantation and placental development.More recently, it was discovered that CSF-1 and its receptor CSF1R are implicated in the mammary gland during normal development and neoplastic growth.