BSP constitutes ~11%–15% of the non-collagenous proteins in bone,66,67 in stark contrast to its much lower levels in dentin, where it accounts for less than 1%.67 Beyond bone, BSP has also been detected at low levels in trophoblast cells of the placenta,4,64 as well as in macrophages and tubular cells of the kidney.68 In the pancreas, BSP expression has been observed in islet, ductal and smooth muscle cells.69 Interestingly, BSP is also expressed in (osteotropic) cancer. The gene discussed is IBSP; the disease is cancer.