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on how to make uniform the measurements of solid component size in many part-solid tumors7). These include not only typical GGO-dominant or solid- dominant part-solid tumors including multifocal expression, but atypical part-solid lesions such as GGO with scattered consolidations9) (Figure 4A and 4B), GGO with island shaped consolidations28, 29) (Figure 4C and 4D), or GGO mimicking organizing pneumonia27) (Figure 4E and 4F).All the more, there exists more critical and fundamental issue in the classification of lung cancer staging. Based on the previous background, we always deem whether it is necessary to classify the prognosis of part-solid lung cancer with a GGO based on the solid component size. Again, clinico-pathological and oncological features are signifi-cantly different between part-solid tumor with GGO and solid tumor without GGO. Therefore, we proposed to classify the current T staging to the subgroup based on the presence or absence of GGO (i.e., GGO group and Solid group). As a result, the 5y-OS was distinct in pure-solid tumor without GGO, which was worse based on the tumor size. However, the prognosis of part-solid tumor with a GGO component was not significantly different regardless of the solid component size, and their Figure 3　Proposed 8th edition of the cT and pT descriptor classifications of small lung adenocarcinomas with a GGO and lepidic component by computed tomography and pathologic diagnosis7).prognosis was excellent, which was irrespective of the current T staging12) (Figure 2). This fact is extremely important when considering future revi-sion of the clinical T staging of lung cancer, provided that the clinicopathologic and oncologic outcomes are disparate between part-solid and pure-solid tumors on the basis of a GGO presence. Recently, this concept has been gradually noticed not only in Japan but several other countries30-35). Despite single institution advocacy for the prog-nostic importance of the presence of a GGO compo-nent as a significant clinical T parameter, however, this notion has not been fully confirmed across institutions or at a nationwide level. To validate this fundamental and simple prognostic feature of lung cancer, we aimed to demonstrate the prog-nostic impact of the presence of a GGO component in clinical stage IA NSCLC based on the long-term follow-up data of JCOG020115). As a result, signifi-cant center validation also suggested the favorable prognostic impact of the presence of a GGO compo-nent in the prospective JCOG0201 dataset. The principle behind the TNM staging system is the classification of cancers into groups according to the anatomic extent. This contributes to eval-uate treatment strategies and to give some indica-55