Significance of elevated ERK expression and its positive correlation with EGFR in Kazakh patients with esophageal squamous cell carcinoma

Extracellular signal-regulated kinases (ERKs) are activated by the MAPK pathway. ERKs are downstream effectors of the epidermal growth factor receptor (EGFR), which belongs to the receptor tyrosine kinases family. Studies on the activation of the EGFR-ERK pathway in Kazakh patients with esophageal squamous cell carcinoma (ESCC) have not been reported. Using immunohistochemical staining on tissue microarrays, we investigated the protein expression of EGFR and ERK in 90 ethnic Kazakh patients with ESCC and 48 adjacent normal esophageal tissues (NETs). EGFR and ERK1 expression was localized in the cytoplasm, whereas ERK2 expression was localized in the nucleus. Both were more highly expression in the ESCC tissues than in the NETs, and the difference was considered significant (P = 0.003, 0.002, and 0.005, respectively). ERK1 and EGFR expression was positively correlated with lymph nodes metastasis (P = 0.011 and 0.013, respectively). ERK1 staining was also significantly associated with tumor-node-metastases stage of ESCC (P = 0.044). ERK2 staining was significantly associated with Histological grade (P = 0.012). Furthermore, ERK1 and EGFR expression in the ESCC tissues were positively correlated (r = 0.413, P < 0.001); EGFR was more highly expressed in the ESCC tissues with high ERK1 expression than in the ESCC tissues with low ERK1 expression (4.95 ± 0.57 vs. 3.21 ± 0.35, P = 0.01). This study is thus far the first to demonstrate the correlation between EGFR overexpression and ERK overexpression in Kazakh patients with ESCC. This correlation suggests that the EGFR-ERK signaling pathway participates in ESCC progression and can thus be used as a prognostic marker.