[Incidence and Characteristics of Mismatch Repair Protein Deficiency in Elderly Gastric Cancer Patients].

The loss of mismatch repair(MMR)function as a result of MLH1 promoter methylation is closely correlated with high frequency microsatellite instability, and tumors with such characteristics are resistant to anticancer drugs such as 5-FU. We examined the incidence and characteristics of deficient MMR(dMMR)in elderly gastric cancer patients by performing a comprehensive immunohistochemical screening. The study was conducted in 199 patients diagnosed with gastric cancer, aged 75 years or older, who underwent a gastrectomy between April 2005 and January 2014. dMMR was detected in 23 patients(12%). All the tumors with dMMR were deficient in MLH1 and PMS2. dMMR was significantly more common compared to proficient MMR(pMMR)in patients with a more advanced age(p=0.03), women(p<0.01), and a tumor location corresponding to the lower region(p<0.01). Considering the incidence of dMMR in elderly gastric cancer patients, only a limited proportion of patients are likely to be eligible for immune checkpoint inhibitor therapy, which is expected to become more popular in the near future.