A study on 44 patients with MiNEN (mean age of 61 years; 63.6% gastric MiNEN) explored IHC for MLH1, MSH2, MSH6, and PMS2: a lack of MMR protein expression was identified in 38.6% of them (most frequent: 29.4% for MLH1/PMS2, respective of 23.5% for MLH1); MMR deficiency versus normal MMR status correlated with a better prognosis in MiNEN [68]. This evidence concerns the gene MSH2 and hyperinsulinemic hypoglycemia, familial, 4.