BAFF-R expression is absent in most HMCLs,38, 50 but has been reported to be variably present in primary MMCs,10, 38, 40, 41, 43, 44, 45, 50, 51, 52, 53 albeit at significantly lower levels than the expression of both BCMA and TACI.43 The discrepancy between the expression of BAFF-R in HMCLs and primary MMCs could be explained by the fact that HCMLs are often cultured from an extramedullary MMC in late stage MM. This evidence concerns the gene TNFRSF13B and Miyoshi myopathy.