Reduced Claudin-3 Expression Is Linked to Unfavorable Tumor Features and Poor Prognosis in Non-Small Cell Lung Cancer.

Background: Claudin 3 (CLDN3) is a transmembrane protein which forms tight junctions (TJs) together with other claudins, occludin, and junctional adhesion molecules. Because of its membranous localization CLDN3 is a potential therapeutic target. Altered CLDN3 has been proposed as a prognostic feature in lung cancer and other tumors. Material and Methods: To better understand the prevalence of expression and its impact on the prognosis of different lung cancer subtypes, we investigated CLDN3 expression by immunohistochemistry in a set of tissue microarrays containing 858 resected lung cancers. Results: CLDN3 positivity was markedly more frequent and more intense in pulmonary adenocarcinoma (AC, 95.9% positive) than in squamous cell carcinoma (SCC, 53.3%; p<0.0001). Among 444 ACs, CLDN3 staining was strong in 64.2%, moderate in 25.0%, weak in 6.8% and negative in 4.1%. In 214 SCCs, CLDN3 staining was strong in 6.1%, moderate in 11.7%, weak in 35.5% and negative in 46.7%. Reduced CLDN3 staining was significantly linked to advanced pT stage in both AC and SCC (p<0.0001 each). The fraction of strongly positive cases decreased markedly from pT1 (AC: 67.6%; SCC: 11.1%) to pT4 (47.2%/1.8%). Low CLDN3 expression was also linked to nodal metastasis (p=0.0339) and R+ status (p = 0.0068) in SCCs. Absent or reduced CLDN3 staining was significantly associated with shortened overall survival in pulmonary ACs (p=0.0235) and SCCs (p=0.0330). Conclusion: It is concluded that CLDN3 expression is common in lung cancer, that its level of expression is higher in AC than in SCC, and that a reduced expression level is associated with unfavorable outcome in both SCC and AC. Once anti-CLDN3 targeted drugs should prove to be safe and efficient, NSCLC may represent a major application for such treatments.