Reclassification and subtyping of so-called malignant fibrous histiocytoma of bone: comparison with cytogenetic features

In the present study, the cytogenetic data on 11 of these tumors (three myoepithelioma-like sarcomas, two leiomyosarcomas, one undifferentiated pleomorphic sarcoma with incomplete myogenic differentiation, two undifferentiated pleomorphic sarcomas, one osteosarcoma, one spindle cell sarcoma, and one unclassifiable biphasic sarcoma) are presented.All tumors were high-grade lesions and showed very complex karyotypes. Neither the overall pattern (ploidy level, degree of complexity) nor specific cytogenetic features distinguished any of the subtypes. The subgroup of myoepithelioma-like sarcomas was further investigated with regard to the status of the EWSR1 and FUS loci; however, no rearrangement was found. Nor was any particular aberration that could differentiate any of the subtypes from osteosarcomas detected.chromosome banding analysis is unlikely to reveal potential genotype-phenotype correlations between morphologic subtypes among so-called MFH of bone.Only some decades ago, malignant fibrous histiocytoma (MFH) was considered the most common soft tissue sarcoma among adults. However, with the introduction of more stringent morphologic and immunohistochemical criteria, it turned out that it was possible to reclassify the vast majority of those tumors as, e.g., poorly differentiated leiomyosarcomas or dedifferentiated liposarcomas [1]. For the few cases in which no signs of differentiation could be discerned, the term undifferentiated pleomorphic sarcoma (UPS) was introduced [2,3]. Importantly, the subclassification of MFH tumors into different lineages of differentiation was shown to be of prognostic significance, with immunohistochemical expression of smooth muscle actin (incomplete myogenic differentiation) being associated with worse outcome [4].In the latest edition of the WHO classification of soft tissue and bone tumors [2], the new view on MFH tumors was introduced for the soft tissue lesions [3], but not for bone tumors [5]. According to the WHO description