Can (18)F-NaF PET/CT before Autologous Stem Cell Transplantation Predict Survival in Multiple Myeloma?

There is an unmet need for positron emission tomography (PET) radiotracers that can image bone disease in multiple myeloma (MM) in a more sensitive and specific way than the widely used (18)F-fluorodeoxyglucose ((18)F-FDG). Sodium fluoride ((18)F-NaF) is a highly sensitive tracer of bone reconstruction, evolving as an important imaging agent for the assessment of malignant bone diseases. We attempted to investigate for the first time the prognostic significance of (18)F-NaF PET/CT in newly diagnosed, symptomatic MM patients planned for autologous stem cell transplantation (ASCT). Forty-seven patients underwent dynamic and static PET/CT with (18)F-NaF before treatment. After correlation with the respective findings on CT and (18)F-FDG PET/CT that served as reference, the (18)F-NaF PET findings were compared with established factors of high-risk disease, like cytogenetic abnormalities as well as bone marrow plasma cell infiltration rate. Furthermore, the impact of (18)F-NaF PET/CT on progression-free survival (PFS) was analyzed. Correlation analysis revealed a moderate, significant correlation of the (18)F-NaF parameters SUV(average) and K(1) in reference tissue with bone marrow plasma cell infiltration rate. However, no significant correlation was observed regarding all other (18)F-NaF PET parameters. Survival analysis revealed that patients with a pathologic (18)F-NaF PET/CT have a shorter PFS (median = 36.2 months) than those with a physiologic scan (median = 55.6 months) (p = 0.02). Nevertheless, no quantitative (18)F-NaF parameter could be shown to adversely affect PFS. In contrast, the respective analysis for quantitative dynamic (18)F-FDG PET/CT revealed that the parameters SUV(max), fractional blood volume (V(B)), k(3) and influx from reference tissue as well as SUV(average) from MM lesions had a significant negative impact on patient survival. The herein presented findings highlight the rather limited role of (18)F-NaF PET/CT as a single PET approach in MM.