Molecular and immunohistochemical profiling of inflammatory infiltrate distinguishes conventional dedifferentiated liposarcoma from dedifferentiated liposarcoma with heterologous differentiation

Background: Liposarcomas account for approximately 20% of all mesenchymal malignancies. Among the entities comprised in this group, the most common is the subgroup related to MDM2 amplification, namely well-differentiated liposarcoma/atypical lipomatous tumour (WDLPS/ALT) and dedifferentiated liposarcoma (DDLPS). In particular, DDLPS is an aggressive mesenchymal malignancy with high rates of local recurrence and metastatic potential. Some studies suggest that both histological grading and heterologous differentiation have a prognostic impact on patient survival. Among those, rhabdomyoblastic differentiation appears to have the poorest prognosis in overall patient survival. In addition, investigating the immune status of DDLPS may have a predictive value for the implementation of treatment for this type of tumour. Evaluation and quantification of T cells, B cells, macrophages, and tertiary lymphoid structures as potential biomarkers play a role in predicting clinical outcomes and response to immune checkpoint inhibitors (ICI) therapy. A more comprehensive understanding of the tumour microenvironment may facilitate the implementation of other immunotherapy strategies. Aim of the study: The aim of this study is to characterise the molecular profile of primary dedifferentiated liposarcomas of various sites, including dedifferentiated liposarcomas with heterologous differentiation, and to evaluate the immune landscape in this heterogeneous group of liposarcomas. Materials and methods: From 2018 to 2023, we selected 22 cases of patients affected by DDLPS from the archives of Padua University Hospital and the consultation cases of Prof. A. P. Dei Tos. Molecular characterisation was performed using NGS RNA sequencing to analyse transcriptomic tumour signatures in all samples. Additionally, in a subset of samples (n =16), lymphocytic and histiocytic tumour infiltration was immunohistochemically characterised using an essential cluster of differentiation markers (CD20, CD3, CD8, CD68, CD14 and CD163). Results: The case series comprised 22 primary cases of DDLPS: 6 rhabdomyoblastic DDLPS, 5 myogenic DDLPS, 1 DDLPS with homologous differentiation and 10 conventional DDLPS. Primary localisations included the retroperitoneum (81%), the spermatic cord (9%), the mediastinum (5%) and the mesentery (5%). The RNA sequencing results showed that rhabdomyoblastic DDLPS represents a transcriptomically distinct subgroup of DDLPS, characterised by elevated levels of miogenesis gene expression and an overall lower inflammatory infiltrate than any other heterologous differentiation case or conventional DDLPS. Interestingly, conventional DDLPS did not show significant transcriptomic differences compared to DDLPS with homologous and myogenic differentiation. The transcriptomic data were validated by immunohistochemistry, which showed a significantly lower density of CD3, CD68 and CD163 in the rhabdomyoblastic DDLPS than in the non-rhabdomyoblastic group (p ≤ 0.05). Conclusions: The obtained results indicate that rhabdomyoblastic DDLPS are immunologically colder than myogenin-negative cases. This could influence the disease aggressiveness and patient survival. Conversely, the presence of an increased immune infiltrate in myogenin-negative DDLPS patients could represent a potential application of targeted immunotherapy. Analysis of the immune context is only the first step to allow a broader therapeutic management of these patients. The preliminary results of the present study were obtained from a limited case series and require validation in larger cohorts.