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

PET with 18 F-FDG is the standard modality in nuclear medicine for imaging multiple myeloma (MM). However, viable MM as detected by MRI or PET with other metabolic tracers, including 11 C-methio-nine, may be missed—for example, because of low hexokinase 2 (HK2) 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 pretreated patients with relapsed or refractory biopsy-proven, serologically active MM who underwent both 18 F-FDG and 11 C-methionine PET/CT was retrospectively analyzed. Results: In 9 of the 15 patients, 18 F-FDG PET was negative in the presence of viable disease. In the remaining 6 patients, both 18 F-FDG and 11 C-methionine PET/CT revealed the same number of MM lesions. At immunohistochemistry, 18 F-FDG–negative myeloma did not exhibit significant differences in HK2 or glucose-6-phosphatase expression from 18 F-FDG–positive disease (P 5 0.57 and P 5 0.44, respectively). Conclusion: Beyond HK2 expression, 18 F-FDG negativity in (mainly pretreated) MM patients seems to be associated with additional causes not yet known.