Development of early treatment strategies for high-risk myeloma precursor disease in the future

Smoldering myeloma (SMM) is a precursor state of multiple myeloma. It is defined by an M-protein concentration ≥3 g/dL and/or ≥10% clonal bone marrow plasma cells, in the absence of end-organ damage. Based on clinical observations, the natural history of SMM varies greatly, from stable, monoclonal gammopathy of undetermined significance (MGUS)-like disease to highly progressive disease. Using conventional clinical markers, SMM patients can be stratified into clinical risk groups. However, due to considerable molecular heterogeneity, we currently lack reliable markers to predict prognosis for individual SMM patients. Based on the International Myeloma Working Group 2010 guidelines, patients diagnosed with MGUS and SMM should not be treated outside of clinical trials. Overall, treatment trials for MGUS patients are complicated, as these individuals are relatively healthy and the majority has a low life-time risk of progression, especially when other causes of death are taken into account. In contrast to MGUS, early treatment strategies for SMM are particularly attractive, as the rate of progression to multiple myeloma is substantially higher. Until recently, potent drugs with reasonable toxicity profiles have not been available for the development of early multiple myeloma treatment strategies. This review discusses how the integration of novel biological markers and clinical monitoring of SMM could facilitate the development of early treatment strategies for high-risk SMM patients in the future.