PGR and breast cancer: Further studies on MCF-7 breast cancer cells and ovariectomized animals showed that arsenite and cadmium increased the global expression of estrogen-responsive genes such as the progesterone receptor (PgR), growth regulation by estrogen in breast cancer 1 (GREB1), and c-fos in the mammary gland, as well as the expression of complement C3, c-fos, and cyclin D1 in the uterus [15].