INTRODUCTION: Lung cancers can display immune cell infiltration although the role of an adaptive immune response in disease pathogenesis is unknown. To investigate the possibility of a functional humoral response to the tumor, we surveyed histologic sections from non-small cell lung cancer (NSCLC) tumors for germinal centers (GCs) and assessed whether there was an association between the presence of GCs and tumor stage. METHODS: Tumor sections from 91 patients with all stages of NSCLC were examined by a pathologist blinded to clinical data. GCs were identified by hematoxylin and eosin staining patterns and confirmed by immunohistochemical staining for B-cell markers, BCL-6 and CD21. The distribution of GCs within the tumor or the tumor margin was recorded. Statistical analysis was performed to evaluate the association between stage and presence of GCs. RESULTS: Thirty-five percent of all tumors evaluated contained GCs, and sections evaluated by immunohistochemistry showed positive staining for both B-cell markers. GCs were seen both within the tumor and the tumor margin, consistent with an immune response to antigen stimulation. Patients with stage I NSCLC had a higher prevalence of intratumoral GCs than patients with stages II to IV (Cochran-Armitage Trend Test p = 0.02011). There was no association of stage with GCs in the tumor margin. CONCLUSIONS: Intratumoral GCs are associated with early-stage NSCLC. Further characterization of intratumoral GCs may lead to new diagnostic and therapeutic strategies based on manipulation of the adaptive immune response.