Marrow uptake on FDG PET/CT is associated with progression from smoldering to symptomatic multiple myeloma

Objective: To determine association of body composition measurements on CT and PET with progression of smoldering myeloma to multiple myeloma. Methods: A retrospective cohort study in 65 patients with smoldering myeloma and PET/CT at diagnosis was performed at a tertiary cancer center. Subjects were between 38 and 87 years of age (mean 64) and included 37 males. Primary outcome was progression-free survival as a function of bone, fat, and muscle metrics on CT and PET (measured at the level of L4 pedicles) and clinical confounders. CT metrics included attenuation of L4 and retroperitoneal fat and various indices derived from the psoas muscle. PET measures included SUV_max and SUV_mean of L4, retroperitoneal fat, and psoas. Cox proportional hazards modeling was performed with entry and retention criteria of p < 0.1 and p < 0.05, respectively. Results: SUV_max and SUV_mean were associated for each compartment (R² = 0.78–0.84), and SUV_mean (SUV) was used for subsequent analyses. SUV of the L4 vertebral body was associated with attenuation of the L4 vertebral body (p = 0.0032). There was no association between SUV and CT for muscle and fat compartments. In the subset of patients with bone marrow biopsy results (n = 43), there was no association between SUV of L4 and plasma cell concentration on core biopsy or flow cytometry (p = 0.089 and 0.072, respectively). The final Cox model showed association with albumin (HR 0.29, 95%CI 0.088–0.93, p = 0.038), M protein (HR 1.31, 95%CI 1.021–1.68, p = 0.034), and SUV of L4 (HR 1.99, 95%CI 1.037–3.82, p = 0.039). Conclusion: SUV of L4 is a prognostic indicator in patients with smoldering myeloma.