Interleukin-10 (IL-10) may play an important role in controlling tumor growth and metastasis. Some reports have shown that IL-10 can be a potent inhibitor of tumor growth, but others suggest that IL-10 expression by the tumor is an adverse prognostic factor. Because normal bronchial epithelial cells constitutively produce IL-10, we decided to test the prognostic value of IL-10 in a well-defined population of patients with stage I non-small cell lung cancer (NSCLC) treated in a single

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... . Using immunohistochemical analysis, we retrospectively analyzed IL-10 expression in specimens from 138 patients with completely resected clinical/radiographic stage I NSCLC for whom clinical follow-up data were available. IL-10 expression was retained (IL-10 labeling index > or = 10%) in 94 patients (68.1%) and lost in 44 patients (31.9%). The duration of overall, disease-specific, and disease-free survival in the 44 patients lacking IL-10 expression was worse than in the 94 patients with IL-10 expression (P = 0.08, 0.02, and 0.05, respectively; Log-rank test). Interestingly, IL-10 expression was observed more frequently in tumors with squamous cell histology than in tumors of other histological subtypes (P = 0.04; chi(2) test). Multivariate analysis confirmed the independent prognostic value of IL-10 expression for disease-specific survival (P = 0.04). Lack of IL-10 expression by the tumor was associated with a significantly worse outcome of early stage NSCLC. The mechanisms underlying this clinically and biologically important finding need to be further explored.