The role of electron microscopy in the diagnosis of pleomorphic sarcomas of soft tissue

Classification of pleomorphic malignancies is frequently problematic and important with regard to treatment. Their histologic differential diagnosis is extremely wide, including sarcomatoid carcinoma, melanoma, anaplastic lymphoma, and a large number of sarcomas with overlapping light microscopic appearances. Not infrequently, immunohistochemical investigations of such tumors yield conflicting or confusing results. In such cases, electron microscopy remains an invaluable investigative and diagnostic adjunct, revealing certain subcellular features that indicate a specific line of differentiation. Combining ultrastructural and immunohistochemical studies is particularly useful in these tumors. This article focuses on the ultrastructural aspects of certain sarcomas that are predominantly pleomorphic, including high- grade fibrosarcoma, myxofibrosarcoma-malignant fibrous histiocytoma, acral myxoinflammatory fibroblastic sarcoma, pleomorphic liposarcoma, pleomorphic leiomyosarcoma, and pleomorphic rhabdomyosarcoma, as well as certain sarcomas that are occasionally quite pleomorphic, including angiosarcoma, malignant granular cell tumor, alveolar soft part sarcoma, and extraskeletal osteosarcoma. We also briefly comment on the common simulators of pleomorphic sarcomas, including melanoma, carcinoma, and lymphoma.