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.