Does malignant transformation of benign soft-tissue tumours occur? A clinicomorphological study of ten initially misdiagnosed soft-tissue sarcomas.

Ten soft-tissue sarcomas out of a consecutive series of 201 neoplasms are described, in which the clinical histories were suggestive of malignant transformation of a benign lesion excised from the same location 2-97 months before. Each of the 10 preceding soft-tissue neoplasms was reviewed histologically and reclassified as either highly (n = 8) or moderately differentiated (n = 2) sarcomas. Irrespective of the primary treatment, these initially misdiagnosed tumours showed an overall better prognosis than the whole group of soft-tissue sarcomas (5- and 10-year survival rates 76% versus 44%, and 52% versus 30% respectively). Their clinical course was, however, characterized by up to 6 (mean 2.9) local recurrences. From the total series of 201 tumours the authors conclude that soft-tissue sarcomas other than malignant schwannomas in the setting of von Recklinghausen's disease only exceptionally, if ever, arise from benign precursors.