Expression patterns of PAX5, c-Met, and paxillin in neuroendocrine tumors of the lung

c-Met is important in the pathogenesis, invasion, and spread of several forms of lung cancer, and multiple c-Met inhibitors are undergoing clinical trials. PAX5 has been shown to upregulate c-Met in small cell lung carcinoma (SCLC), and coinhibiting PAX5 and c-Met had a synergic effect in killing tumor cells. Paxillin is a downstream target of activated c-Met, and its activation leads to enhanced cell motility and tumor spread. The expression patterns of these functionally related proteins have not, to our knowledge, been systemically studied in neuroendocrine tumors of the lung. Objective.-To investigate the expression patterns of PAX5, paxillin, c-Met, and phosphorylated c-Met in 4 categories of pulmonary neuroendocrine tumors. Design.-Tissue microarrays of 38 typical carcinoids, 6 atypical carcinoids, 34 SCLCs, and 11 large cell neuroendocrine carcinomas were studied with immunohistochemistry. Results.-Most of the 4 tumor types expressed c-Met, phosphorylated c-Met, and paxillin. PAX5 was frequently expressed in atypical carcinoids, SCLCs, and large cell neuroendocrine carcinomas but tended to be negative in typical carcinoids. Coexpression of PAX5 with c-Met or phosphorylated c-Met was present in most of the atypical carcinoids, SCLCs, and large cell neuroendocrine carcinomas. Significant correlation between PAX5 and paxillin was detected in SCLCs and large cell neuroendocrine carcinomas but not in carcinoid tumors. Conclusions.-The frequent coexpression of PAX5 with c-Met or phosphorylated c-Met in intermediate-grade and high-grade neuroendocrine tumors supports the therapeutic strategy of coinhibiting these proteins. The discrepancy between high-grade and low-grade neuroendocrine tumors in PAX5/paxillin expression correlation may be due to the different underlying molecular genetics of these tumors.