Embryo implantation and tumor metastasis: common pathways of invasion and angiogenesis.

Implantation of the embryo is one of the last great mysteries of reproductive biology. There are striking similarities present between the behavior of invasive placental cells and that of invasive cancer cells. In this review, we propose that cellular mechanisms used by the cells of the placenta during implantation are reused by cancer cells to invade and spread within the body. Integrins and other cell adhesion molecules, extracellular matrix and matrix metalloproteinases all appear to be involved and are regulated by the complex endocrine, autocrine and paracrine milieu within the uterus. Angiogenesis is a common feature of both implantation and cancer spread. Endothelial cells also use similar cellular mechanisms during angiogenesis to digest the surrounding matrix, migrate and form new blood vessels. A better understanding of the mechanism of trophoblast invasion will likely lead to insights of various diseases of pregnancy such as preeclampsia. An appreciation of the maternal mechanisms to control this invasive behavior may likewise lead to a better understanding of metastatic cancer cells and lead to better methods to control their growth and spread within host tissues.