Well-differentiated and dedifferentiated liposarcomas with prominent myxoid stroma: analysis of 56 cases.

AIMS: Occasional cases of well-differentiated and dedifferentiated liposarcoma (LPS) contain myxoid stroma, leading to confusion with other sarcomas. The aim of this study was to analyse the clinicopathological and genetic features of well-differentiated/dedifferentiated LPS with prominent myxoid stroma.

METHODS AND RESULTS: Fifty-six cases of LPS (22 well-differentiated; 34 dedifferentiated) with prominent myxoid stroma were evaluated. Most arose in the retroperitoneum, abdominal cavity, or spermatic cord. The mean size was 170 mm. Myxoid LPS-like plexiform vessels were conspicuous in 11 cases of well-differentiated LPS. In 22 cases of dedifferentiated LPS, myxofibrosarcoma-like curvilinear vessels were prominent. In other cases, the myxoid component had variably bland or pleomorphic morphology. By immunohistochemistry, staining for MDM2 was positive in 95% of cases, and CDK4 in 78%. Cytogenetics in 13 cases showed ring and giant marker chromosomes. Fluorescence in-situ hybridization showed amplification of 12q13-15 in six cases evaluated. Of 30 patients with follow-up, all but one had local recurrences (up to four), but only one has so far had distant metastases.

CONCLUSIONS: Well-differentiated/dedifferentiated LPS with prominent myxoid stroma can closely resemble other sarcoma types, especially myxoid LPS and myxofibrosarcoma. The clinical presentation (large retroperitoneal or abdominal tumour) is a clue to the correct diagnosis; the degree of nuclear atypia helps to exclude myxoid LPS. Immunohistochemistry for MDM2 and CDK4 and genetic analysis can be useful to confirm the diagnosis.