PTK7 and esophageal squamous cell carcinoma: Furthermore, in the clinical tumor samples we examined, positive or strong positive staining of PTK7is correlated with most tumor samples but not with normal adjacent tissues (Fig. 1b, χ2test, p < 0.001), strongly arguing for an oncogenic role of PTK7 in the tumorigenesis of human esophageal squamous cell carcinoma.