Biological Significance of Dedifferentiation of Sarcomas

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After reviewing the microscopic slides and clinical summaries of a collection of 1085 cases of soft tissue sarcomas registered at the Second Department of Pathology, Kyushu University Faculty of Medicine, we selected 27 instances of so-called "Differentiated" Soft Tissue Sarcoma (DSTS), defined as well or moderately differentiated sarcoma containing additional anaplastic areas indistiguishable from malignant fibrous histiocytoma or fibrosarcoma. These included 14 (11%) selected from 128 liposarcomas, six (6%) from 105 leiomyosarcomas, five (13%) from 39 extraskeletal chondrosarcomas, and two (2%) from 98 rhabdomyosarcomas. In addition to the clinicopathologic study, we conducted an immunohistochemical survey of 23 cases and an electron microscopic examination of three. The findings were compared with observations of 32 cases of de novo malignant fibrous histiocytoma (MFH). All tumors contained additional distinct anaplastic portions indistinguishable from MFH under conventional light microscopy, ultrastructurally, and in cases of immunoreactivity for alpha-l-antichymotrypsin and alpah-l-antitrypsin and on lectin histochemical findings for ricinus communis agglutinin and concanavalin agglutinin. The anaplastic components of DSTS are presumed to represent the proliferation of another clone of undifferentiated mesenchymal cells that fail to differentiate along any specific lineage other than fibroblast-like cells, histiocyte-like cells, and myofibroblasts. This concept alsoleads to the proposal that de novo MFH is a primitive mesenchymal tumor without any specific differentiation.According to follow-up data, the prognosis of patients with DSTS was ominous. Nineteen of the 27 patients died of the tumor.