Smouldering Multiple Myeloma (SMM)

The definition of Smouldering Multiple Myeloma (SMM) was revised in 2014 and requires two criteria to be met:

1. The presence of a serum monoclonal protein (IgG or IgA) at a concentration of ≥30 g/L or a urinary monoclonal protein ≥500 mg/24 hours and/or 10-60% clonal bone marrow plasma cells (BMPCs)

2. The absence of myeloma defining events (including an involved/uninvolved Freelite serum free light chain (FLC) ratio of ≥100 or Amyloidosis

Guidelines recommend that serum FLCs are measured at baseline for all SMM patients to allow risk stratification.

A highly abnormal serum FLC ratio at baseline is associated with a substantial risk of progression to active Myeloma (MM).

Asymptomatic patients with an involved/uninvolved serum FLC ratio of ≥100* in conjunction with ≥10% clonal bone marrow plasma cells or biopsy-proven plasmacytoma are now classified as having MM requiring treatment.

*involved Freelite concentration must be ≥100 mg/L