Dedifferentiated liposarcoma with homologous lipoblastic differentiation: expanding the spectrum to include low-grade tumours

Aims Dedifferentiated liposarcoma (DDLPS) is traditionally defined as a non‐lipogenic high‐grade sarcoma arising from a well‐differentiated liposarcoma that confers metastatic potential. Recently, DDLPSs with lipoblastic differentiation, i.e. morphologically lipogenic DDLPSs, were reported. Because of the lipoblastic differentiation, these tumours caused confusion, and were reported under different names. However, cytogenetic and molecular studies have revealed their DDLPS nature. So far, the cases reported have been high‐grade pleomorphic liposarcoma‐like tumours. In this study we have collected another series that contains low‐grade tumours, and expand the histological spectrum. Methods and results Eighteen cases of DDLPS with lipoblastic differentiation from various anatomical locations were analysed by routine histology, immunohistochemistry, and MDM2 fluorescence in‐situ hybridization. Two main histological patterns were seen: one featured a spindle cell sarcoma containing lipoblasts with variable nuclear pleomorphism, and the other a pleomorphic liposarcoma‐like tumour including the epithelioid variant. Two cases showed low nuclear grade and lipogenic activity in the metastatic foci. CDK4, MDM2 and p16INK4a overexpression was seen in all except one case. MDM2 amplification was found in all 16 cases tested. Conclusions We have expanded the spectrum of this variant of DDLPS to include low‐grade tumours, in which a careful search for increased mitotic activity is essential. Like conventional DDLPS, these tumours are capable of metastasis.