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

Abstract

Background

Despite the significant upgrading in recent years of the role of ¹⁸F-FDG PET/CT in multiple myeloma (MM) diagnostics, there is a still unmet need for myeloma-specific radiotracers. 3′-Deoxy-3′-[¹⁸F]fluorothymidine (¹⁸F-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 ¹⁸F-FLT PET/CT in imaging of MM patients, in the context of its combined use with ¹⁸F-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 ¹⁸F-FDG PET/CT and ¹⁸F-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. ¹⁸F-FDG PET/CT demonstrated focal, ¹⁸F-FDG avid, MM-indicative bone marrow lesions in five patients. In contrary, ¹⁸F-FLT PET/CT showed focal, ¹⁸F-FLT avid, myeloma-indicative lesions in only two patients. In total, 48 ¹⁸F-FDG avid, focal, MM-indicative lesions were detected with ¹⁸F-FDG PET/CT, while 17 ¹⁸F-FLT avid, focal, MM-indicative lesions were detected with ¹⁸F-FLT PET/CT. The number of myeloma-indicative lesions was significantly higher for ¹⁸F-FDG PET/CT than for ¹⁸F-FLT PET/CT. A common finding was a mismatch of focally increased ¹⁸F-FDG uptake and reduced ¹⁸F-FLT uptake (lower than the surrounding bone marrow). Moreover, ¹⁸F-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 ¹⁸F-FLT than for ¹⁸F-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 ¹⁸F-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.

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