CXCL12 and monoclonal gammopathy: demonstrated, by immunohistochemistry, that BM in which PCs are present show increased expression of CXCL-12 [also known as stromal cell-derived factor 1 (SDF-1)], compared to samples from healthy controls or patients with monoclonal gammopathy of undetermined significance (MGUS), which showed minimal and low expression of SDF-1 (9).