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To examine the expression of the transcription factor nuclear factor kappa B (NF-κB) in Barrett's epithelium and adenocarcinoma and the impact of NF-κB expression on tumor stage and response to neoadjuvant chemotherapy and radiation therapy.Progression of Barrett's esophagus to adenocarcinoma is associated with a wide range of cellular and molecular abnormalities. Nuclear factor-kappa B (NF-κB) regulates several genes involved in inflammatory, immune and apoptotic responses, but its role in esophageal inflammation and tumorigenesis has not been reported.Mobility shift assay was used to measure NF-κB activity in nuclear extracts of fresh-frozen biopsies from tumor and uninvolved tissues (n = 30) and esophageal cell lines OE33, SKGT-4, and OE21. RelA expression was assessed by immunohistochemical staining (n = 97). The NF-κB/RelA and IκB protein expressions were also examined by Western blotting.NF-κB was not expressed in normal esophageal squamous epithelium, in contrast to increased expression in 40% of patients with Barrett's epithelium. Sixty-one percent of resected tumors (n = 97) displayed NF-κB immunoreactivity, and 87.5% of the NF-κB- positive tumors were Stage IIb and III compared with only 12.5% of patients with Stage I and IIa disease (P < 0.05). The expression of NF-κB inversely correlated with major or complete pathologic responses to neoadjuvant chemotherapy and radiation therapy, with 15/20 (75%) responders in the NF-κB-negative group compared with 7/38 (18%) in the NF-κB-positive group (P < 0.00001). Moreover, incubation of esophageal cell lines OE33, SKGT-4, and OE21 with deoxycholic acid or low pH induced NF-κB expression.Bile acids and low pH induce NF-κB expression in esophageal cell lines. NF-κB activation is common in esophageal adenocarcinoma. In patients with Barrett's epithelium and an associated esophageal adenocarcinoma, there is a progressive expression of NF-κB through Barrett's tumorigenesis. The absence of NF-κB expression in esophageal adenocarcinoma correlates with response to neoadjuvant chemoradiotherapy and may be of value in predicting response to neoadjuvant therapy.