In multivariate analysis, the presence of plasmacytoma (HR 3.990, 95%CI 1.328–11.986, P = 0.014) and elevated serum β2-microglobulin (HR 2.942, 95%CI 1.030–8.398, P = 0.044) were significant predictors of OS. This evidence concerns the gene HLA-G and plasmacytoma.