This case highlights that constitutional MLH1 methylation should be considered in the differential diagnosis for a polyposis syndrome if IHC staining shows absent MMR gene expression.
Lynch syndrome (Hereditary non-polyposis colorectal cancer/HNPCC) is a cancer susceptibility syndrome which is caused by germline mutations in DNA mismatch repair (MMR) genes, in particular MLH1 and MSH2.
The eponymous Muir-Torre syndrome (MTS) is a clinical variant of hereditary non polyposis colorectal cancer, and is defined as an autosomal dominant condition with simultaneous sebaceous neoplasms of the skin and visceral malignant disease resulting from germline mutations in the DNA mismatch repair (MMR) genes.
Occurrence of childhood tumors in hereditary cancer syndromes such as BRCA1/2 associated breast and ovarian cancer, DNA-mismatch repair (MMR) genes associated hereditary non polyposis colorectal cancer and CDKN2A associated familial malignant melanoma are very little studied.