Abstract
Purpose: Soft tissue sarcomas (STS) account for less than 1% of all malignancies and constitute a heterogeneous tumor entity in which malignant fibrous histiocytomas (MFH) represent one-third and are characterized by a lack of type-specific differentiation. A defective mismatch repair (MMR) system cause the familial cancer syndrome hereditary non-polyposis colorectal cancer (HNPCC), and since occasional MFH have been described in HNPCC patients we assessed the contribution of defective MMR to the development of MFH.Methods: MMR status was characterized in a series of 209 histopathologically reviewed MFH. Tissue microarray sections from the tumors were immunohistochemically stained for the MMR proteins MLH1, MSH2 and MSH6, and cases with aberrant staining were further characterized for microsatellite instability.Results and Discussion: Two of the 209 STS–a storiform-pleomorphic MFH and a myxofibrosarcoma–showed concomitant loss of MSH2 and MSH6, but retained staining for MLH1 on both cases. The myxoid tumor also had a microsatellite unstable phenotype. These findings, together with previous observations of defective MMR in pleomorphic STS, indicate that these tumors may be part of the HNPCC-associated tumor spectrum and demonstrate that MMR defects occur in a small subset of STS.
Highlights
Soft tissue sarcomas (STS) are rare with an incidence of 20–25 per million
Thereafter, 202 tumors were determined to have normal retained immunostaining for all three antibodies, two tumors showed loss of expression for MSH2 and MSH6, with retained staining for MLH1, and five tumors were non-evaluable due to poor staining quality or lack of staining in the internal control
The 20-cm storiform-pleomorphic malignant fibrous histiocytoma (MFH) developed in the left thigh of a 96-year-old woman
Summary
There are more than 50 histological subtypes of STS, and with increased use of ancillary techniques, such as electron microscopy and immunohistochemical staining, a line of differentiation can be identified in most STS. This development has had particular consequences for malignant fibrous histiocytoma (MFH). MFH was introduced as a specific STS subentity, with fibroblastic appearance but of proposed histiocytic origin, during the 1960s.1. MFH quickly became the most common STS entity, with the two most common subtypes being the pleomorphic-storiform and the myxoid types.[2] Since its introduction, there has been intense debate among pathologists with a special interest in STS regarding the histogenesis, or line of differentiation shown by MFH and many of these tumors show heterogeneous morphology and multiple, often complex, cytogenetic aberrations.[2,3]
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