Hexokinase-2 Expression in MET-positive FDG-negative Multiple Myeloma.

Positron emission tomography (PET) with 18 F-fluorodeoxyglucose (18 F-FDG) is the standard modality in nuclear medicine for imaging multiple myeloma (MM). However, viable MM as detected by magnetic resonance imaging or PET with other metabolic tracers including 11 C-methionine (11 C-MET) may be missed by this technique, e.g. due to low hexokinase-2 expression of tumor cells. The aim of this study was to further investigate potential reasons for PET "false-negativity". Methods: A cohort of 15 mainly pre-treated, relapsed/refractory patients with biopsy-proven, serologically active MM who underwent both 18 F-FDG- and 11 C-MET-PET/CT was retrospectively analysed. Results: In 9/15 patients, 18 F-FDG-PET was negative in the presence of viable disease. In the remaining 6 subjects, both 18 F-FDG - and 11 C-MET-PET/CT revealed the same amount of MM lesions. At immunohistochemistry, 18 F-FDG-negative myeloma did not exhibit significant differences in hexokinase-2 or glucose-6-phosphatase expression as compared to 18 F-FDG-positive disease ( P = 0.57 and P = 0.44, respectively). Conclusion: Beyond HK2 expression, 18 F-FDG negativity in (mainly pre-treated) MM patients seems to be associated with additional, yet unknown causes.