PTEN and hyperinsulinemic hypoglycemia, familial, 4: A further example of crosstalk between PTEN and other pathways in regulating sensitivity/resistance to therapeutic immune checkpoint targeting is the interaction between PTEN expression and DNA mismatch repair (MMR): in a report focusing on PTEN immunohistochemistry (IHC) as a diagnostic tool for the screening of MMR-proficient breast cancer, PTEN-integrity seems to represent a protective factor against MMR deficiency in breast cancer [127].