¹¹C-methionine-PET in multiple myeloma : Correlation with clinical parameters and bone marrow involvement

Multiple myeloma (MM) remains an essentially incurable hematologic malignancy originating from clonal plasma cells. This study evaluated the usefulness of the radiotracers ¹¹C-methionine (MET) and ¹⁸F-2'-deoxy-2'-fluorodeoxyglucose (FDG) for staging and re-staging in MM. 43 patients with MM underwent both MET- and FDG-PET/CT for staging or re-staging within 3±2 days. Scans were compared on a patient and on a lesion basis. Tracer uptake was correlated with the degree of bone marrow (BM) involvement and standard clinical parameters of disease activity. Additionally, BM samples were stained for L-type amino acid transporter 1 (LAT1) expression in 15 patients. MET-PET detected focal lesions (FL) in 39/43 subjects (90.7%), whereas 10 patients were missed in FDG-PET/CT (detection rate, 33/43; 76.7%; p < 0.05). MET depicted more FL in 28/43 patients (65.1%; p < 0.001), whereas in the remainder (34.9%, n=15) both tracers yielded comparable results. LAT1 was highly expressed on the cell surface of myeloma cells. Both FDG and MET uptake correlated significantly with biopsy-proven BM involvement (p < 0.001), with MET demonstrating a stronger correlation (SUVmₑₐn, r=0.9 vs r=0.6; SUVmₐₓ, r=0.88 vs r=0.58). Abnormal beta-2-microglobulin and free light chain levels correlated with the presence of focal intramedullary lesions detected in MET- or FDG-PET/CT (MET, p=0.006 and p=0.01, respectively; FDG, p=0.02 and p=0.01). MET appears to be superior to FDG for staging and re-staging of both intra- and extramedullary MM lesions. Tracer uptake correlates with BM involvement, ß2m and FLC levels and appears to be a more accurate marker of tumor burden and disease activity. CA Extern