Unexpected normal serum beta-microglobulin (B2M) levels in multiple myeloma.

Measuring serum beta-2-microglobulin (B2M) in 90 patients with multiple myeloma (MM) from diagnosis to death (83 cases), or to the terminal phase of their disease (7 cases), we have obtained evidence that 9% of them retained normal serum B2M levels during the whole of their follow-up. This was observed in 6 IgA MM, in one light chain MM only and in one non-secretory MM. These data suggest a lack of B2M production and/or secretion by some myeloma tumors. This could limit the use of B2M as clinical marker in MM.