Atypical identification of Lynch syndrome by immunohistochemistry and microsatellite instability analysis on jejunal adenocarcinoma.

As we learn more about the etiology and cancer risks associated with Lynch syndrome (LS), the phenotypic spectrum of this condition and its genotype-phenotype correlations are being elucidated. We report a patient with past history of multiple cancers including colon and kidney cancer, and recently diagnosed with jejunal adenocarcinoma. The patient had microsatellite instability and immunohistochemistry (MSI/IHC) testing performed on his small bowel cancer in order to evaluate his risk for LS. The MSI/IHC results on his tumor tissue were reported as abnormal and subsequent blood draw revealed the presence of a germline MSH6 mismatch repair gene mutation. This case highlights the phenotypic variability of LS and complications it may present in evaluation for diagnosis and appropriate surveillance and management recommendations. To our knowledge, this is the first report of MSI/IHC being done on small bowel cancer to evaluate for this condition and subsequently confirmed via molecular analysis.