Introduction: T4 lung cancer is a heterogeneous group of locally advanced disease. We hypothesized that patients in whom T4 lung cancer invaded only mediastinal fat tissue would show better prognosis after surgery than patients in whom T4 disease invaded other organs. The present study aimed to investigate how different invasive features of T4 disease impacted prognosis, and what types of patients with T4 disease could benefit most from surgical treatment. Methods: A nationwide registry study on lung cancer surgical cases during 2004 was conducted by the Japanese Joint Committee of Lung Cancer Registry, including registries of 11,663 cases within Japan. The present study analyzed 215 of these cases involving T4 structures or with ipsilateral nonprimary lobe pulmonary metastasis (PM). Results: Reasons for T4 classification included invasion of only mediastinal tissue in 32 cases (15%), invasion of other structures in 96 cases (45%), and ipsilateral different lobe PM in 87 cases (40%); among these three groups, there were no significant differences in survival, nodal status, and patterns of first recurrence. Multivariate analysis showed an age of 70 years or above (p = 0.022) and nodal status (p = 0.004) to be significant prognostic factors. T4N0 patients less than 70 years of age showed significantly better prognosis than those who were T4N1-2 and 70 years of age or older (p = 0.0001; 5-year survival rate 50.3 versus 19.9%). Conclusions: There was no significant difference in survival between T4 patients with only mediastinal fat invasion and those with other T4 organ invasion and ipsilateral different lobe PM, demonstrating appropriateness of the T4 category definition in the current tumor, node, metastasis staging system. Age and nodal status were significant independent prognostic factors in T4 patients, and the best surgical candidates were shown to be T4N0 patients who were less than 70 years of age and had a 5-year survival rate of more than 50%.
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