Purpose: Up-regulation of the receptor tyrosine kinase EphA2 has been shown in several epithelial cancers. Epidermal growth factor receptor (EGFR) and K-Ras have been reported to regulate EphA2 in several in vitro models, but this regulation has never been examined in tumors from patients. Because of the established importance of EGFR and K-Ras mutations in non^small cell lung cancer (NSCLC), we investigated the relationship between these mutations and EphA2 in this cancer type. The significance of EphA2 expression was further examined by testing for correlation with other clinical parameters. Experimental Design: EphA2 expression was analyzed by immunohistochemistry in tissue microarray format using surgically resected NSCLC specimens (n = 279). EGFR and K-Ras mutation status was determined for most specimens. The correlation between EphA2 expression and EGFR or K-Ras mutation status was examined, along with several clinicopathologic variables of the tumors. The effects of increasing EGFR and K-Ras activity on EphA2 expression and activity were examined in two cell lines.Results: EphA2 expression was detected in >90% of tumor samples. Expression of EphA2 was positively correlated with activated EGFR but not with EGFR mutations. EphA2 expression was increased in patients harboring K-Ras mutations. EphA2 expression was positively correlated with a history of smoking, and high EphA2 scores predicted poorer progression-free and overall survivals. Conclusions: EphA2 expression in NSCLC is associated with K-Ras mutations, EGFR activation, smoking history, and poor prognosis. EphA2 expression is up-regulated in the context of EGFR or K-Ras activation. The potential of EphA2 as a therapeutic target for NSCLC should be further investigated.Lung cancer is the leading cause of cancer-related death both in the United States and worldwide. Although novel approaches have improved survival in certain subsets of patients with the most common form of lung cancer, nonsmall cell lung cancer (NSCLC), the overall 5-year survival rate associated with NSCLC is only f15%. To improve our understanding of NSCLC, we investigated the role of a potential new biomarker and therapeutic target, EphA2, in the context of known clinical and molecular characteristics of NSCLC. To date, no one has undertaken an examination of the relationship between EphA2 and the Ras/Raf/extracellular signal-regulated kinase (ERK) pathway in NSCLC or in patient tumors.The remarkable differences in the molecular, epidemiologic, and clinical features of NSCLC in smokers compared with nonsmokers show that these are two distinct diseases (1). Approximately 85% of NSCLC cases are associated with smoking. Two of the most common proteins that are activated and/or mutated in NSCLC, epidermal growth factor receptor (EGFR) and K-Ras, are related to smoking in different ways. Dysregulated EGFR signaling has been shown to contribute to several tumorigenic processes, including proliferation, invasion, metastasis, apoptosis, and angiogenesis (2, 3). Activating EGFR mu...