FN1 and breast cancer: The signature of BRGs ectopically coexpressed in breast cancer tissues mainly includes genes encoding matrix proteins that are expressed at the early stages of bone differentiation, e.g., collagens, SPARC/OSN, and fibronectin (FN), but does not include the matrix proteins expressed at a nonreversible differentiation stage, e.g., alkaline phosphatase (ALP), or those expressed in mature osteoblasts and terminally differentiated osteocytes, e.g., bone sialoprotein (BSP), decorin, and osteocalcin (OC)20,22.