Baseline global splenic uptake of FDG in multiple myeloma patients: a higher uptake is associated with inferior overall survival

Objectives: At presentation, multiple myeloma (MM) is mostly limited to the bone marrow, and extramedullary involvement is rare but associated with advanced stage and aggressive activity. The spleen is one of the most common sites of malignant plasma cell infiltration outside of the bone marrow. In this study, we measured the global uptake of FDG in the entire spleen of MM patients at baseline by applying a novel method of global quantification. Also, we aimed to assess the relationship between global SUVmean (GSUVmean) in the spleen and survival data.

Methods: Thirty-eight MM patients (n= 38, 12 females, 26 males, mean age 66 ± 8 years, range 50-87) were collected from the FULIMA study approved by the Danish National Committee on Health Research Ethics registered at ClinicalTrials.gov [NCT02187731]. The patients were followed for up to 55 months (median 40, range 3-55) after treatment. The DICOM viewer was used to draw regions of interest on fused FDG PET/CT images, including the spleen and excluding surrounding tissues (OsiriX, Pixmeo SARL, Bernex, Switzerland). A weighted average of SUVmean was calculated. The SUVmean was multiplied by the entire volume of spleen. Kaplan-Meier curves and Cox regression analyses were used to evaluating the association between splenic GSUVmean and overall survival (OS) and progression-free survival (PFS).

Results: A cut-off value of 320.6 was obtained from ROC analysis. A splenic GSUVmean higher than 320.6 was associated with inferior OS (log-rank p=0.047). In univariate Cox regression analysis, a higher splenic GSUVmean was a significant predictor of inferior OS (HR: 7.04, 95% CI: 0.79-68.77; p= 0.04). Multivariate Cox regression analyses failed to show a significant correlation for any parameters. The results for PFS were not significant.

Conclusions: Higher splenic global uptake of FDG at baseline was associated with lower OS in MM patients. Importantly, many patients did not have focal sites of FDG avidity in the spleen, implying that splenic GSUVmean is able to express the severity of disease even in the absence of abnormally localized FDG foci at this extramedullary site.