Malignant fibrous histiocytoma: morphologic pattern or pathologic entity?

Since the concept of malignant fibrous histiocytoma (MFH) was introduced and subsequently popularized in the 1960's and 1970's, it has become widely regarded as the commonest soft-tissue sarcoma of adulthood. Although the initial notion that MFH was a true histiocytic tumor showing faculative fibroblastic differentiation has been disproved, and despite the lack of definable, reproducible diagnostic criteria and considerable immunophenotypic, ultrastructural and karyotypic heterogeneity, MFH is still accepted widely as a discrete clinicopathologic entity. On the other hand several recent studies have expressed considerable doubts about MFH, or at least pleomorphic MFH, as an "entity" and have suggested that it represents a common morphologic manifestation of a host of poorly differentiated sarcomas and, more rarely, other neoplasms. This article reviews the clinicopathologic features of MFH and its established variants in the context of this debate and considers the evidence for and against their continued acceptance as distinct entities or as a cohesive group. We conclude that the pleomorphic, giant cell and inflammatory variants each represent heterogeneous diagnostic groups which are hard to defend as cohesive entities, while the myxoid ("myxofibrosarcoma") and angiomatoid types are distinct, reproducible tumor types.