HDAC9 and CDH1-related diffuse gastric and lobular breast cancer syndrome: In conclusion, our study has demonstrated that E-cadherin-deficient gastric and breast cells are more sensitive to HDAC inhibitors than their wild-type isogenic pairs and suggests that that pan-HDAC inhibitors—in particular, entinostat—may have a role in the chemoprevention of HDGC and the treatment of sporadic LBC and DGC.