[Does malignant fibrous histiocytoma exist?]

Malignant fibrous histiocytoma (MFH) has come to be regarded as the most common malignant neoplasm of the mesenchymal soft tissues. It designates a spectrum of tumors which share morphologic features that allow their inclusion in a distinct clinicopathologic setting, although being not uniform in their histogenesis and pathogenesis. Clinicopathologic variants include the following: the storiform-pleomorphic form of MFH, the myxoid type of MFH, the giant cell type of MFH and the inflammatory type. The latter group, the angiomatoid variant, has been reclassified within the fibrohistiocytic tumors of low malignant potential. Tissue culture, ultrastructural and immunohistochemical studies have both endorsed or refuted the validity of the concept. As a whole, these morphologic studies which attempted to characterize MFH were not able to delineate specific markers or to describe the phenotype of this sarcoma of supposed fibrohistiocytic lineage. There is growing evidence that MFH is a second component in another sarcoma and represents a morphologic modulation resulting from tumor progression. Recent cytogenetic and molecular genetic investigations are consistent with that hypothesis: a comparative analysis between the most frequent genomic imbalances observed in series of MFH and leiomyosarcomas (LMS) demonstrated that both tumors had similar recurrent imbalances. Immunohistochemical and molecular biologic investigations have shown similar targets of chromosome deletions in both tumors. A new classification of soft tissue sarcoma based on molecular parameters is nevertheless premature. The morphologic characterization of MFH and its sub-types provides the clinician with unique information in the management of these tumors, by identifying a spectrum of tumors with well-recognized clinical profiles.