Prognostic Impact of Tumor Size Eliminating the Ground Glass Opacity Component: Modified Clinical T Descriptors of the Tumor, Node, Metastasis Classification of Lung Cancer

Introduction: The presence of ground glass opacity (GGO) on high-resolution computed tomography (HRCT) is well known to be pathologically closely associated with adenocarcinoma in situ. Recently, measuring the tumor diameter including areas of GGO on HRCT has been reported to possibly overestimate the T status. The purpose of this study was to evaluate the significance of the tumor size measured eliminating the area of GGO on HRCT as a prognostic factor and to propose a refined TNM classification based on modified T descriptors. Methods: Four hundred seventy-five patients with clinical T1a-T2bN0M0 non-small-cell lung cancer underwent surgical resection. All tumors were reclassified based on the diameter measured eliminating the GGO area on HRCT according to the seventh TNM classification of lung cancer. We defined this new classification as modified T descriptors categorizing into five groups: mTis, mT1a, mT1b, mT2a, and mT2b. The overall survival rates of the patients in the current and modified staging groups were evaluated. Results: The 5-year survival rates were 88% and 82% in the patients with T1a and T1b tumors and 90% and 75% in the patients with mT1a and mT1b tumors, respectively. The differences in the survival rate of the patients classified by using mT1a and the other modified T descriptors were more clearly separated statistically than those of the patients classified by using the current T1a and other T descriptors. Conclusion: The modified T descriptors of the tumor size measured eliminating the GGO component on HRCT more clearly classified the prognoses of patients with early lung cancer than did the current T classification.