The Immune Contexture of Liposarcoma and Its Clinical Implications

SIMPLE SUMMARY: Liposarcomas (LPS) are malignancies arising from adipose tissue. Based on the histological appearance, five subtypes are distinguished: well-differentiated LPS, dedifferentiated LPS (DDLPS), myxoid LPS (MLPS), pleomorphic LPS, and myxoid pleomorphic LPS. Immune cells can infiltrate the tumor microenvironment (TME) of LPS and can either promote an efficient antitumor immune response or mediate immunosuppression paving the way for immune evasion of the tumor. The LPS subtypes display different TME characteristics and vary in regard to immune cell infiltration, ranging from the generally lowly infiltrated MLPS to the highly infiltrated DDLPS where immunological determinants predict response to novel antibody-based immunotherapy. Thus, immune cells in the TME can significantly affect response to therapy, disease progression, and patient survival. This review aims to decipher the immune contexture of LPS as well as its clinical association and highlights differences between the LPS subtypes that may have implications for the design of novel treatment strategies. ABSTRACT: Liposarcomas (LPS) are the most frequent malignancies in the soft tissue sarcoma family and consist of five distinctive histological subtypes, termed well-differentiated LPS, dedifferentiated LPS (DDLPS), myxoid LPS (MLPS), pleomorphic LPS, and myxoid pleomorphic LPS. They display variations in genetic alterations, clinical behavior, and prognostic course. While accumulating evidence implicates a crucial role of the tumor immune contexture in shaping the response to anticancer treatments, the immunological landscape of LPS is highly variable across different subtypes. Thus, DDLPS is characterized by a higher abundance of infiltrating T cells, yet the opposite was reported for MLPS. Interestingly, a recent study indicated that the frequency of pre-existing T cells in soft tissue sarcomas has a predictive value for immune checkpoint inhibitor (CPI) therapy. Additionally, B cells and tertiary lymphoid structures were identified as potential biomarkers for the clinical outcome of LPS patients and response to CPI therapy. Furthermore, it was demonstrated that macrophages, predominantly of M2 polarization, are frequently associated with poor prognosis. An improved understanding of the complex LPS immune contexture enables the design and refinement of novel immunotherapeutic approaches. Here, we summarize recent studies focusing on the clinicopathological, genetic, and immunological determinants of LPS.