The purpose of this study was to identify risk factors for disease recurrence and unfavorable prognosis after surgical resection for stage I non-small cell lung cancer in patients with tumor diameters of Յ20 mm. Methods: One hundred sixty-three patients who had pathologic stage I non-small cell lung cancer with tumor diameters Յ20 mm and who had undergone a lobectomy with mediastinal lymph node dissection were retrospectively reviewed. The relationships between clinicopathologic factors and

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... ical outcomes, including recurrence and survival, were then examined. The clinicopathologic factors examined in this study were age, sex, smoking status, preoperative serum carcinoembryonic antigen level, pathologic tumor size, histologic subtype, histologic grade, and visceral pleural invasion. Results: Among the clinicopathologic factors that were examined, the histologic grade of the carcinoma status was significantly related to a high risk of recurrence when analyzed using univariate (p ϭ 0.01) and multivariate analyses (p ϭ 0.049). Regarding survival, patients with poorly differentiated carcinomas showed a significantly unfavorable overall survival (p Ͻ 0.001), disease-specific survival (p ϭ 0.003), and disease-free survival (p ϭ 0.002) compared with patients with well-/moderately differentiated carcinomas according to univariate analyses. A Cox proportional hazards model indicated that a poorly differentiated carcinoma status was the only independent factor for an unfavorable overall survival (p ϭ 0.02), disease-specific survival (p ϭ 0.046), and disease-free survival (p ϭ 0.04). Conclusions: Poor differentiation of tumor was the only risk factor for recurrence and an unfavorable prognosis for stage I non-small cell lung cancer patients with tumor diameters of Յ20 mm. FIGURE 2. Crude survival curves stratified according to well, moderately, and poorly differentiated histologic grade. (A) Overall survival. (B) Disease-specific survival. (C) Disease-free survival.