Smoldering multiple myeloma: pathophysiologic insights, novel diagnostics, clinical risk models, and treatment strategies

Abstract

Smoldering multiple myeloma (SMM) is a plasma cell disorder first described in 1980 when 6 patients were observed to meet the diagnostic criteria of multiple myeloma, defined as bone marrow plasmacytosis of 10% or greater or M protein level of 3 g/dL or greater, but did not have end-organ damage. Subsequent studies showed that the cumulative risk of SMM progression to symptomatic myeloma in 15 years was 73%. Since this time, advances have been made in understanding the biology of progression; namely, the contribution of branching evolution and microenvironment models to clonal heterogeneity. In parallel to this, clinical risk models using standard platforms of serum, bone marrow, and fluorescence in situ hybridization markers along with newer technologies of flow cytometry, gene expression profiling, and magnetic resonance imaging have been developed for prognostic stratification. Treatment has extended to the early myeloma category owing to more sensitive diagnostic approaches. The development of novel treatments will have to take into consideration our current knowledge of biological transformation. While it may be attractive to initiate early treatment in light of recent studies for high-risk SMM patients, clinical trial evidence of efficacy vs toxicity is still in its infancy. In our opinion, high-risk SMM patients should be strongly encouraged to enroll in treatment clinical trials, but treatment with unapproved agents or indications is not supported outside of trials.