PTK2 and esophageal squamous cell carcinoma: We first evaluated whether CAFs can affect the tumor inhibitory effect of FAK inhibitors, including defactinib and VS4718, using ESCC cell lines/CAFs (five cases of CAFs) coculture system in transwell apparatus with 0.4 μm pore size, and then tumor cells (in the lower chamber of transwell plates) were subjected to MTS assay (Fig. 1a).