Temporal trends in progression risk in smoldering myeloma: a systematic review.

Background: Diagnostic advancements and classification updates appear to have reshaped the natural history of smoldering multiple myeloma (SMM), though this evolution has not been empirically quantified. We conducted a systematic review to evaluate temporal changes in SMM prognosis. Methods: PubMed, EMBASE and the Cochrane library databases were searched from January 1990 to November 2025, yielding 1415 reports, of which 14 studies met inclusion criteria. To reconstruct individual-level data, published time to progression (TTP) curves were digitized using a Shiny web application. Kaplan-Meier (KM) survival curves and meta-analyses were generated in RStudio. PROSPERO ID 1068697. Findings: Progression risk at two and ten years for all-risk patients was 22.8% and 60.1%, respectively; these increased to 44.7% and 85.6% in high-risk patients. Landmark analysis from year five revealed attenuated progression rates: 14.2% and 30.8% for all-risk, and 22.5% and 50.6% for high-risk patients at two and five years post-landmark, respectively. Studies enrolling most patients before 2014 showed higher progression rates than in more recent cohorts (Spearman's rho = 0.645, p = 0.034), but this trend did not reach statistical significance in high-risk groups (rho = 0.360, p = 0.272). Meta-analytic data further supported elevated progression in older cohorts. Interpretation: SMM appears to follow a more indolent trajectory in recent years, likely due to improved diagnostic precision and exclusion of biomarker-defined or subclinical MM. Enhanced predictive models may better guide therapeutic decision-making, targeting treatment to those most likely to benefit and avoiding the burden of unnecessary intervention in low-risk individuals. Funding: Supported by the Austrian Forum Against Cancer.