Refining PET-based response in extramedullary multiple myeloma using total lesion glycolysis

Positron Emission Tomography (PET)-based assessments are an integral part of response assessment in patients with multiple myeloma (MM) with extramedullary disease (EMD), yet their utility in EMD remains to be systematically studied. We retrospectively evaluated 95 patients with EMD undergoing FDG PET/CT imaging for metabolic response assessment using visual Deauville Scores (DS) and total lesion glycolysis (TLG). TLG responses were categorized as complete metabolic response (CMR; 100% reduction), major metabolic response (MMR; <100% to ≥50% reduction), and non-significant metabolic response (NMR; <50% reduction). The median progression-free survival (PFS) differed significantly by DS (22.4 vs. 4.3 vs. 2.8 months for DS ≤ 3, =4, and =5, respectively; p < 0.0001) and by TLG response (36.5 vs. 5.4 vs. 2.2 months for CMR, MMR, NMR; p < 0.0001). TLG offered better discrimination than DS, with approximately one-third of patients in each DS stratum being reclassified by the TLG stratification. In a multivariable analysis, TLG response [HR 2.6 (95% CI: 1.8-3.8), p < 0.0001] remained independently prognostic after adjusting for cytogenetics, triple-class refractoriness, and de novo EMD status. The 18-month OS rates were 89%, 42% and 19% for the TLG CMR, MMR, and NMR cohorts (p < 0.001). These findings support the integration of TLG into response criteria for EMD.