Association of a duodenal follicular lymphoma and hereditary nonpolyposis colorectal cancer

Hereditary nonpolyposis colorectal cancer (HNPCC) is an inherited predispos ition to colorectal and endometriaI cancers caused by germline mutation of mismatch repair genes, with hMLH1 and hMSH2 underlying the majority of the cases. Although lymphoid tumors are the most common tumors in mouse models far HNPCC, lymphomas are almost never encountered in patients who have HNPC C, except in rare families with germline homozygous deletion of ;HI. We rep ort the case of a 53-year-old man who had a history of colon cancers relate d to constitutional mMLH1 mutation and who was diagnosed as having a duoden al follicular lymphoma. This diagnosis was supported by IgH-BCL2 rearrangem ent and BCL2 immunoreactivity in turner cells. The association of both of t hese possibly related rare diseases has never been reported. To clarify thi s relationship, we searched for hMLH1 expression and mismatch repair defici ency in the duodenal lymphoma hMLH1 immunostaining was positive in lymphoid tumor cells, and no microsatellite instability was detected. In agreement with mouse models for HNPCC, these results suggest the involvement of alter native mechanisms to complete mismatch repair deficiency for lymphomagenesi s in HNPCC syndrome.