Osteogenic differentiation in dedifferentiated liposarcoma: a study of 36 cases in comparison to the cases without ossification

Aims Ossification is occasionally found in dedifferentiated liposarcoma (DDLPS). The aims of this study were to elucidate whether the formed bone tissue is usually produced by tumor cells or by reactive non-neoplastic cells, and to reveal the clinicopathological characteristics of DDLPS with ossification. Methods and results We examined 36 cases of ossified DDLPS by comparing them to 31 cases of non-ossified DDLPS. MDM2 amplification was confirmed in osteocytes and/or osteoblastic cells in all but one ossified DDLPS cases (27/28) using fluorescence in-situ hybridization, although morphological impression of ossification was mostly metaplastic looking (27/36) or high grade osteosarcoma like (6/36). The bone tissue was often predominantly formed at the periphery of the DDLPS area near the well-differentiated liposarcoma component (18/36), and an organized structure such as bone marrow-like differentiation was not uncommon (12/36). According to a modified French Federation Nationale des Centers de Lutte Contre le Cancer (FNCLCC) grading system, ossified DDLPS tended to be lower grade than non-ossified DDLPS (mean grade of 1.88 and 2.15, respectively). Ossification in DDLPS was significantly associated with shorter local recurrence free survival by the multivariate analysis (P = 0.02347), but metaplastic-looking ossification tended to be associated with longer overall survival (P =0.1400). Conclusions The bone tissue formed in DDLPS was mostly neoplastic regardless of its morphology and maturity, which highlighted the osteogenic differentiation of the tumor cells. DDLPS patients with osteogenic differentiation tended to suffer from earlier local recurrences, which did not necessarily lead to poor life outcomes. This article is protected by copyright. All rights reserved.