The usefulness of 18F-FDG PET to discriminate between malignant and benign nodule in patients with underlying idiopathic pulmonary fibrosis

Abstract

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Objectives: Due to the high incidence of lung cancer development, detecting pulmonary nodule in idiopathic pulmonary fibrosis (IPF) is important. However, it is difficult to discriminate malignant nodule from benign nodule by means of chest CT in patients with underlying IPF. The aim of this study was to evaluate the diagnostic performance of FDG PET to differentiate malignancy from benign nodule in patients with underlying IPF.

Methods: A total of 28 lung nodules from 16 subjects with underlying IPF were enrolled (age; 67.5±9.8, M:F=14:2). Diagnostic criteria for malignancy were size, morphology and serial change in chest CT. FDG PET was visually interpreted and maxSUV was calculated for quantitative analysis. Diagnosis of malignancy was confirmed by histopathology (n=6) and/or follow-up imaging studies (n=22).

Results: There were 10 malignant nodules (squamous cell carcinoma: 6, adenocarcinoma: 4) and 18 benign nodules. MaxSUV of malignant lung nodules were higher than that of benign nodules (7.7±4.0 vs. 1.2±0.7, p<.001). Using cut-off value of 2.6, sensitivity and specificity of FDG PET were 100% and 94.4%, respectively (AUC on ROC curve=0.989 , p<.01). Underlying IPF lesion showed mildly elevated maxSUV of 1.8±0.4, which might be associated with disease activity of IPF. The size measured by chest CT was 24.0±10.2 mm in malignant nodule, and 10.8±5.2 mm in benign nodule (p<.01). The overall sensitivity and specificity of CT considering size, morphology and serial change were 66.7% and 44.4%, respectively. Diagnostic accuracy of FDG PET tended to be higher than that of chest CT.

Conclusions: FDG PET showed superior diagnostic performance to chest CT in differentiating lung nodules in patients with underlying IPF. FDG PET could be used to differentiate lung nodule detected by chest CT in patients with underlying IPF.