CLDN1 and gastrointestinal stromal tumor: Moreover, we observed that FGF-2 ligand increased expression of CLDN1 in IM-naive GIST cells in a time-dependent manner (Figure 5A), whereas pan-FGFR inhibitors (e.g., AZD 4547 and TAS-120) decreased CLDN1 expression in IM-resistant GIST T-1R cells (Figure 5B).