Value of integrated positron emission tomography revised using a phantom study to evaluate malignancy grade of lung adenocarcinoma

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The malignant biological behavior of small-sized lung adenocarcinomas remains obscure, although understanding this feature is important for selecting appropriate treatment. In the current study, the authors evaluated malignancy grades of small adenocarcinomas using fluorodeoxyglucose-positron emission tomography/computed tomography (PET/CT) in addition to high-resolution CT (HRCT) and pathological analysis in a multicenter setting. A total of 201 patients with clinical T1N0M0 adenocarcinoma underwent PET/CT and HRCT followed by complete surgical resection. Associations between components of bronchioloalveolar carcinoma (BAC) in specimens and maximum standardized uptake values (maxSUV) on PET/CT and ground-glass opacity (GGO) ratios and tumor disappearance rate (TDR) on HRCT were analyzed, as well as associations between these findings and pathological features of the tumors. Variations in maxSUV among institutions and the underestimations derived from small tumors, which are limitations of PET performed in multicenter studies, were adjusted using a phantom study. The maxSUV, BAC ratio, TDR, and GGO ratio (in that order) reflected the grade of tumor invasiveness and lymph node metastasis. The maxSUV and BAC ratio were found to be significant prognostic predictors derived from disease-free survival curves. Although the BAC ratio was found to be significantly associated with preoperative radiographic parameters, the maxSUV, GGO ratio, and TDR (all P < .0001), the degree of correlation with maxSUV (correlation coefficient [R(2)] = 0.1699) was much weaker than that reported with the GGO ratio (R(2) = 0.5860) or TDR (R(2) = 0.5082). Phantom studies can overcome the difficulties of multicenter studies using PET. A higher maxSUV appears to reflect aggressive malignant behavior in clinical T1N0M0 adenocarcinomas, independent of BAC components. Preoperative PET/CT assessment in addition to HRCT could be used to construct hypotheses for a future clinical study of strategies for the treatment of patients with small lung adenocarcinoma.