Sebaceous Carcinoma : MLH1 expression
Sebaceous carcinomas may present as a component of Muir-Torre syndrome. Such cases show inherited defects in one of the DNA mismatch repair (MMR) genes. The major MMR genes are MLH1 (on chromosome 3p21), MSH2 (on chromosome 2p22), MSH6, and PMS2. The loss of corresponding proteins in Muir-Torre syndrome can be reliably detected with immunohistochemical stains. MSH2 expression is lost in more than 90% of cases. The detection of microsatellite instability and/or loss of MMR proteins in both the cutaneous as well as internal malignancies is highly specific for Muir-Torre syndrome. This image shows intact expression of MLH1 in a patient with Muir-Torre syndrome; however, there was no immunoreactivity for MSH2 and MSH6 (see next two images). Image courtesy of: Marcelo Balancin, MD, Sao Paulo, Brazil.