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. This evidence concerns the gene SPARC and breast cancer.