High-Risk Smoldering Multiple Myeloma: A Review of Controversies in Early Treatment Versus Observation

Abstract

Smoldering multiple myeloma (SMM) is an asymptomatic but biologically heterogeneous plasma cell disorder with a variable risk of progression to multiple myeloma (MM). Accurate risk stratification is essential as only a subset of patients—defined as high-risk SMM —faces a ≥50% risk of progression within 2 years. Contemporary approaches integrating clinical variables, dynamic biomarkers, genomic alterations, and immune profiling have improved risk assessment although some limitations remain. The therapeutic paradigm of SMM is evolving. Randomized phase III trials have consistently shown that early treatment delays progression to MM. Most recently, daratumumab monotherapy became the first approved treatment for high-risk-SMM following the AQUILA trial, which demonstrated a significant progression-free survival benefit (hazard ratio [HR], 0.49 [95% CI, 0.36 to 0.67], P < .001) and a trend toward improved overall survival (OS; HR, 0.52 [95% CI, 0.27 to 0.98]) versus observation. This approval challenges the traditional watch-and-wait approach and establishes early intervention as a validated option for selected patients. However, important uncertainties persist. With modern surveillance and advanced imaging, most progression events are asymptomatic and irreversible end-organ damage is uncommon. OS benefit from early treatment remains inconclusive, particularly in the era of quadruplet regimens available at MM progression. In addition, difficulties in precisely identifying truly high-risk patients raise concerns about overtreatment. Emerging data from intensive regimens, bispecific antibodies, and chimeric antigen receptor -T cell therapies suggest that deep and durable responses—and possibly cure—may be achievable in selected patients with high-risk-SMM, but long-term benefit and safety require further study. In conclusion, following the approval of daratumumab, SMM management should be risk-adapted and patient-centered: observation remains appropriate for some patients, while early treatment should be considered for carefully selected high- and ultrahigh-risk individuals.