First Experience of 11C-Methionine PET in Multiple Myeloma in Turkey

A 45-year-old female patient with newly diagnosed immunoglobulin (Ig)G k-type myeloma at stage III of the disease as per the International Staging System was referred for positron emission tomography (PET) imaging to evaluate the extent of the disease. In this patient, the IgG level was 17.8 g/L (reference range: 7.51-15.6 g/L) and kappa free light chain was 3660 mg/L (reference range: 3.3-19.4 mg/L). Bone marrow biopsy showed 80% plasma cells, which were strongly positive for CD38 and CD138. 11C-Methionine (MET) and 18F-fluorodeoxyglucose (FDG) PET/CT images showed discordant findings in the whole body (Figure 1). Whereas PET/CT with FDG did not depict hypermetabolic intra- or extramedullary foci for active multiple myeloma (MM) (range of SUVmax: 1.5-2.9), MET demonstrated focally increased tracer uptake of the axial (Figure 2) as well as appendicular skeleton (range of SUVmax: 14.3-15.4).

Figure 1

MIP images of 11C-MET and 18F-FDG demonstrate discrepant findings in the whole body.

8F-FDG: 8F-fluorodeoxyglucose

Figure 2

FDG depicts faint uptake in the skeleton (range of SUVmax: 1.5-2.9) in contrast to highly intense lesions in 11C-MET (transaxial slice of calvarium, left 4th and right 6th ribs, arrows) (range of SUVmax: 14.3-15.4).

18F-FDG PET/CT is widely used in prognosis estimation and therapy response evaluation in MM [1]. However, in some cases, plasma cells may not be 18F-FDG-avid  [2,3] or may not overexpress the GLUT-1 receptor. Thus, glucose metabolism may not accurately reflect disease heterogeneity, lowering the sensitivity of 18F-FDG PET/CT. 11C-MET PET has emerged recently as a metabolic indicator in 18F-FDG-negative cases. 11C-MET uptake is related to increased plasma cell proliferation and protein synthesis. Both bone marrow and extramedullary involvement can be successfully demonstrated by 11C-MET [4,5]. Availability of 11C-MET is limited worldwide, however, due to the very short half-life of carbon-11 (11C) and the necessity of a PET center with an onsite cyclotron. This first experience in Turkey demonstrates the discrepant results between 18F-FDG and 11C-MET well. It is now possible in our center to follow non-18F-FDG-avid MM cases with 11C-MET.