Microsatellite instability in a pleomorphic rhabdomyosarcoma in a patient with hereditary non-polyposis colorectal cancer.

AIMS

To describe the rare occurrence of a pleomorphic sarcoma with microsatellite instability in a patient with hereditary non-polyposis colorectal cancer (HNPCC).

METHODS AND RESULTS

A soft tissue tumour was removed from the upper leg of a patient who had previously been shown to harbour a germ-line MSH-2 mutation. The tumour was analysed with immunohistochemistry and molecular methods. The morphology and immunohistochemical findings were in keeping with a pleomorphic rhabdomyosarcoma. Microsatellite instability was documented in the tumour with molecular methods and in addition loss of MSH-2 expression in the tumour cells was confirmed by immunohistochemistry.

CONCLUSIONS

Although sarcomas do not form part of the HNPCC diagnostic criteria, they may occur in this mismatch repair syndrome and, moreover, may well be caused by the underlying genetic defect.