(18)F-FDG and (11)C-Methionine PET/CT in Newly Diagnosed Multiple Myeloma Patients: Comparison of Volume-Based PET Biomarkers

(11)C-methionine ((11)C-MET) is a new positron emission tomography (PET) tracer for the assessment of disease activity in multiple myeloma (MM) patients, with preliminary data suggesting higher sensitivity and specificity than (18)F-fluorodeoxyglucose ((18)F-FDG). However, the value of tumor burden biomarkers has yet to be investigated. Our goals were to corroborate the superiority of (11)C-MET for MM staging and to compare its suitability for the assessment of metabolic tumor burden biomarkers in comparison to (18)F-FDG. Twenty-two patients with newly diagnosed, treatment-naïve symptomatic MM who had undergone (11)C-MET and (18)F-FDG PET/CT were evaluated. Standardized uptake values (SUV) were determined and compared with total metabolic tumor volume (TMTV) for both tracers: total lesion glycolysis (TLG) and total lesion (11)C-MET uptake (TLMU). PET-derived values were compared to Revised International Staging System (R-ISS), cytogenetic, and serologic MM markers such as M component, beta 2 microglobulin (B2M), serum free light chains (FLC), albumin, and lactate dehydrogenase (LDH). In 11 patients (50%), (11)C-MET detected more focal lesions (FL) than FDG (p < 0.01). SUVmax, SUVmean, SUVpeak, TMTV, and TLMU were also significantly higher in (11)C-MET than in (18)F-FDG (p < 0.05, respectively). (11)C-MET PET biomarkers had a better correlation with tumor burden (bone marrow plasma cell infiltration, M component; p < 0.05 versus p = n.s. respectively). This pilot study suggests that (11)C-MET PET/CT is a more sensitive marker for the assessment of myeloma tumor burden than (18)F-FDG. Its implications for prognosis evaluation need further investigation.