Sebaceous Neoplasm With Defective DNA Mismatch Repair
A woman in her 70s presented with a cutaneous lesion composed of a mixture of basaloid cells and sebocytes arranged in lobules, most consistent with a sebaceous adenoma (Figure 1). Immunohistochemistry for mismatch repair genes showed loss of nuclear expression of MSH2 and MSH6 in the tumor cells. Representative images are depicted in Figure 2. Microsatellite instability testing showed instability in all of the 7 informative markers analyzed, indicative of defective DNA mismatch repair function within the tumor.