KIT and Miyoshi myopathy: CD117 (proto-oncogene c-KIT) is a receptor tyrosine kinase normally expressed by mast cells and hematopoietic progenitors in the BM, but absent during B-cell maturation from early precursors to PCs.38 This antigen is aberrantly over-expressed in ~70% of MGUS patients and 30% of MM patients.