Assessment of glucose metabolism and cellular proliferation in multiple myeloma: a first report on combined (18)F-FDG and (18)F-FLT PET/CT imaging

BACKGROUND: Despite the significant upgrading in recent years of the role of (18)F-FDG PET/CT in multiple myeloma (MM) diagnostics, there is a still unmet need for myeloma-specific radiotracers. 3′-Deoxy-3′-[(18)F]fluorothymidine ((18)F-FLT) is the most studied cellular proliferation PET agent, considered a potentially new myeloma functional imaging tracer. The aim of this pilot study was to evaluate (18)F-FLT PET/CT in imaging of MM patients, in the context of its combined use with (18)F-FDG PET/CT. RESULTS: Eight patients, four suffering from symptomatic MM and four suffering from smoldering MM (SMM), were enrolled in the study. All patients underwent (18)F-FDG PET/CT and (18)F-FLT PET/CT imaging by means of static (whole body) and dynamic PET/CT of the lower abdomen and pelvis (dPET/CT) in two consecutive days. The evaluation of PET/CT studies was based on qualitative evaluation, semi-quantitative (SUV) calculation, and quantitative analysis based on two-tissue compartment modeling. (18)F-FDG PET/CT demonstrated focal, (18)F-FDG avid, MM-indicative bone marrow lesions in five patients. In contrary, (18)F-FLT PET/CT showed focal, (18)F-FLT avid, myeloma-indicative lesions in only two patients. In total, 48 (18)F-FDG avid, focal, MM-indicative lesions were detected with (18)F-FDG PET/CT, while 17 (18)F-FLT avid, focal, MM-indicative lesions were detected with (18)F-FLT PET/CT. The number of myeloma-indicative lesions was significantly higher for (18)F-FDG PET/CT than for (18)F-FLT PET/CT. A common finding was a mismatch of focally increased (18)F-FDG uptake and reduced (18)F-FLT uptake (lower than the surrounding bone marrow). Moreover, (18)F-FLT PET/CT was characterized by high background activity in the bone marrow compartment, further complicating the evaluation of bone marrow lesions. Semi-quantitative evaluation revealed that both SUV(mean) and SUV(max) were significantly higher for (18)F-FLT than for (18)F-FDG in both MM lesions and reference tissue. SUV values were higher in MM lesions than in reference bone marrow for both tracers. CONCLUSIONS: Despite the limited number of patients analyzed in this pilot study, the first results of the trial indicate that (18)F-FLT does not seem suitable as a single tracer in MM diagnostics. Further studies with a larger patient population are warranted to generalize the herein presented results. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (10.1186/s13550-018-0383-7) contains supplementary material, which is available to authorized users.