PET/CT Characteristics of Isolated Bone Metastases in Hepatocellular Carcinoma

Abstract

To compare the prognostic implications and positron emission tomography (PET)/computed tomography (CT) characteristics of isolated bone metastasis secondary to hepatocellular carcinoma (HCC) with those of HCC metastases to bone and other sites. This study was approved by the institutional ethics committee, and informed consent was obtained from all patients. Extrahepatic metastases were diagnosed in 257 patients with HCC by using dual-tracer (carbon 11 [(11)C] acetate and fluorine 18 fluorodeoxyglucose [FDG]) PET/CT. Metastatic bone lesions were identified with visual inspection and semiquantitative assessment and confirmed with histopathologic examination and/or supported by findings at other radiologic examinations or serial PET/CT. The frequency of bone metastasis from HCC was 19% (49 of 257 patients; eight patients had histopathologic proof and 41 had imaging proof). Metastasis isolated to bone (group 1, 30 of 257 patients [12%]) was more common than metastasis to bone and other sites (group 2, 19 of 257 patients [7%]). At lesion-based analysis of group 1 (71 index lesions; mean lesion size ± standard deviation, 3.25 cm ± 1.88), (11)C acetate PET was more sensitive than FDG PET (93% [66 of 71 lesions] vs 62% [44 of 71 lesions], respectively; P < .05). The combined sensitivity was 97% (69 of 71 lesions) with dual-tracer PET and 72% (51 of 71 lesions) with CT. At patient-based analysis, (11)C acetate PET had an incremental value of 23% (seven of 30 patients) over FDG PET. At lesion-based analysis of group 2, FDG PET was more sensitive than (11)C acetate PET (87% [33 of 38 lesions] vs 50% [19 of 38 lesions], respectively; P < .05). Tracer avidities of metastatic bone lesions were closely correlated with that of their corresponding primary HCC tumors. The median survival time was longer in group 1 than in group 2 (18 months vs 11 months, respectively; P < .05). Isolated bone metastasis from HCC may not be as uncommon as previously believed. The detection of these metastases can be significantly enhanced with (11)C acetate PET compared with FDG PET alone. Identification of this group of patients also seems to have prognostic importance.