Caspase recruitment domain family member 9 expression is a promising biomarker in esophageal squamous cell carcinoma

Abstract Aim Esophageal squamous cell carcinoma (ESCC) is a refractory digestive organ cancer that requires better treatment strategies. We have recently reported that the antidiabetic drug metformin exerts antitumor effects on ESCC by inhibition of nuclear factor kappa B (NF‐κB) nuclear translocation. In the present study, we focused on caspase recruitment domain family member 9 (CARD9), an essential signal adapter in NF‐κB activation to examine whether it can be used as a prognostic factor in ESCC. Methods We investigated CARD9 expression immunohistochemically in clinical samples obtained from 93 patients with ESCC who underwent curative esophagectomy. CARD9 expression was analyzed for correlation with clinicopathological characteristics and ESCC prognosis. The molecular effects were investigated by knocking down ESCC cells. Comprehensive RNA expression changes in these ESCC cells were detected by next‐generation sequencing (NGS). Results High CARD9 expression is significantly correlated with advanced tumor depth (P