CDKN2A and posterior cortical atrophy: Over the last 20 years, there have been a number of immunohistochemical studies of p16 expression in prostate and PCa.23, 24, 25, 26, 27, 28, 29 A variety of antibodies, staining protocols, and scoring systems have been used and studies range in size from several dozen to more than 9000 cancer cases.