Small cell carcinoma: arising in Lynch syndrome: a previously undocumented occurrence.

Lynch syndrome is a genetic cancer predisposition syndrome caused by an inherited defect in 1 of 4 DNA mismatch repair genes (mutL homolog 1, mutS homolog 2, mutS homolog 6, and postmeiotic segregation 2). Despite the theoretically increased risk in all tissues, Lynch syndrome exhibits tissue specificity, with a particular tendency among affected individuals to develop colorectal and endometrial cancer at a young age. A number of other malignancies, including those derived from the ovary, stomach, small bowel, and urothelium, have also been linked to this syndrome. A growing body of evidence exists to support an association between mismatch repair mutations and a growing spectrum of hereditary nonpolyposis colon cancer-associated neoplasms. In this article, a previously undocumented mismatch repair-related malignancy in a patient with Lynch syndrome is reported.