Kircher S, et al. - For imaging multiple myeloma (MM), PET with ¹⁸F-FDG is the standard nuclear medicine modality, so researchers examined possible explanations for PET false negativity via retrospectively analyzing cohort of 15 mostly pretreated patients with relapsed or refractory biopsy-proven, serologically active MM who had both ¹⁸F-FDG and ¹¹C-methionine PET/CT. ¹⁸F-FDG-negative myeloma did not show significant differences in hexokinase 2 (HK2) or glucose-6-phosphatase expression vs ¹⁸F-FDG–positive disease in immunohistochemistry. Beyond HK2 expression, ¹⁸F-FDG negativity in (mostly pretreated) MM patients appears to be linked to unknown additional causes.