Body Composition Metrics Associated with Time to Progression in Smoldering Multiple Myeloma

Objective: To determine the association of body composition (BC) in smoldering multiple myeloma (SMM) with time to progression (TTP) to MM. Methods: The quantity and quality of adipose and muscle tissue were retrospectively derived from 63 whole-body low-dose computed tomography (WBLDCT) scans between 2017 and 2021. BC was analyzed by segmenting a single axial image at the level of the fourth lumbar vertebrae. Subjects were grouped into below vs. above the sex-specific median for BC metrics. Clinical information including TTP and progression risk factors were recorded. Cox proportional hazard models were used to determine the association between BC metrics and TTP. BC groups were compared using the Wilcoxon rank sum test and Fisher's exact test. Results: Thirty subjects progressed over a median follow-up of 49.2 months. For subjects with a subcutaneous adipose tissue (SAT) cross-sectional area (CSA) below vs. above the median, TTP was 24.8 vs. not reached (p = 0.02). Similarly, TTP was 20.7 vs. not reached (p = 0.01) for those with SAT CSA indexed to height below vs. above the median. High SAT CSA (hazard ratio [HR]: 0.42 [95%CI: 0.20-0.90], p = 0.03) and high SAT index (HR: 0.39 [95%CI: 0.18-0.83], p = 0.01) were both associated with a lower progression risk. High SAT index remained significantly associated with reduced progression risk in multivariate analysis (p = 0.03). There was no association between TTP and obesity (BMI ≥ 30 kg/m²) or muscle metrics. High SAT CSA and index were associated with younger age and higher hemoglobin levels. Conclusions: SAT quantity might serve as a prognostic marker for progression in SMM.