Retroperitoneal undifferentiated pleomorphic sarcoma having microsatellite instability associated with Muir-Torre syndrome: case report and review of literature.

[dedifferentiated liposarcoma]

Muir-Torre syndrome represents a rare autosomal dominant familial cancer predisposition disorder defined by the occurrence of cutaneous sebaceous tumors and an internal malignancy , most commonly gastrointestinal carcinoma . Most examples of hereditary non-polyposis cancer syndrome (Lynch syndrome ), including the Muir-Torre syndrome , are associated with microsatellite instability (MSI ) and germline mutations in mismatch repair genes-most commonly MLH 1 or MSH 2 . We present a 58 -year -old man with Muir-Torre syndrome and a large retroperitoneal mass (14 .3 cm in greatest dimension ) encompassing the left adrenal gland . Sections showed a cellular malignant tumor composed of spindle cells with a high mitotic index and lacking morphologic evidence of adipocytic differentiation . It was weakly reactive for smooth muscle actin (SMA ) and negative for desmin , CD 117 , CD 31 , CD 34 , S 100 protein and pan-cytokeratin . Further immunohistochemical analysis revealed intact expression of MLH 1 but loss of MSH 2 in tumor nuclei . Compared to non-neoplastic tissue , the tumor showed MSI in five of seven dinucleotide markers . Fluorescence in situ hybridization (FISH ) failed to reveal 12 q 15 amplification , effectively excluding dedifferentiated liposarcoma as a diagnostic consideration . This is a rare case of a patient with Muir-Torre syndrome who developed a related high -grade undifferentiated pleomorphic sarcoma as the associated internal malignancy .