Development of invasive colon cancer with microsatellite instability in a patient with hyperplastic polyposis syndrome.

The serrated pathway has recently been proposed as a route for the development of colorectal cancer with microsatellite instability. Hyperplastic polyposis syndrome is a rare syndrome defined by the presence of numerous serrated polyps, with a high risk of developing into colorectal cancer. We present here a case of hyperplastic polyposis syndrome developing into colorectal cancer with microsatellite instability from a serrated polyp. BRAF mutation and the loss of MLH1 protein were observed in the colorectal cancer, but not in the other serrated polyps around the colorectal cancer, suggesting that colorectal cancer with microsatellite instability develops rapidly from a specific serrated polyp with distinct molecular properties.