Finally, overexpression of DKK1 in glucocorticoid-induced osteoporosis [18,20,21] as well as in osteosarcoma and osteolytic metastatic bone disease in multiple myeloma [22-24] led to the hypothesis that DKK1 is a strong candidate gene for the regulation of bone homeostasis. This evidence concerns the gene DKK1 and plasma cell myeloma.