Although K8/K18 pairs were previously thought to be expressed only in simple epithelial cells and its derived epithelial tumors, an increasing number of studies have found that abnormal expression of K8/K18 is also present in various squamous cell carcinomas and is associated with tumor invasion, metastasis, and poor prognosis (24, 139, 140). This evidence concerns the gene KRT8 and squamous cell carcinoma.