This cycle is reinforced by the secretion of tumor factors (dickkopf-related protein 1: DKK-1, sclerostin 1: SOST-1, BMP inhibitor noggin, and activin A) inhibiting osteoblast activity, which is manifested by damaged bone with decreased bone mineral density (BMD) [23,24,28,29]. The gene discussed is DKK1; the disease is neoplasm.