The heterogeneity of microsatellite instability in multiple gastric cancers.

To obtain a better understanding of the role of genetic instability in developing gastric cancer, it is of great interest to examine microsatellite alterations in synchronous multiple gastric cancers that are thought may have the same genetic background and the same microenvironment of the stomach. We report our experience with two patients with synchronous multiple gastric cancers; patient 1 showed two carcinomas in the stomach, whereas patient 2 showed two carcinomas and two adenomas in the stomach. We examined the DNAs from the two cases for microsatellite instability and expected that the status of microsatellite instability in each tumor from the same stomach would be the same. However, patient 2 revealed heterogeneity in the microsatellite instability, i.e., an early cancer that showed some apparent alterations, whereas the other advanced cancer and two adenomas did not. On the other hand, neither of the two carcinomas in patient 1 showed microsatellite instability. To our knowledge, there has been no previous report of microsatellite instability in multiple gastric cancers. In this report, we describe a case that revealed such a heterogeneity of the microsatellite instability, in which the carcinogenic process of each tumor may undergo different genetic alterations even under the same genetic conditions and background.