Considerations on the Performance of Immunohistochemistry for Mismatch Repair Gene Proteins in Cases of Sebaceous Neoplasms and Keratoacanthomas With Reference to Muir–Torre Syndrome

Cutaneous sebaceous tumors, as well as keratoacanthomas, are associated with Muir-Torre syndrome (MTS). Visceral neoplasias are a feature of this syndrome; thus, early detection using a cutaneous biopsy is very important in dermatopathology. A dermatopathologist can apply different techniques in such cases, including immunohistochemistry for several mismatch repair proteins or molecular studies for microsatellites instability. However, in a world where economic resources play an increasing role, how discriminative the dermatopathologist should be in investigating cutaneous lesions that may indicate MTS is not a trivial matter. Although previous reports have presented algorithms on MTS focusing on a multidisciplinary approach, our report emphasizes the role of the dermatopathologist and tries to answer several questions that could arise when facing a cutaneous tumor that may indicate MTS.