Single-cell sequencing reveals the landscape of the tumor microenvironment in a skeletal undifferentiated pleomorphic sarcoma patient

Novel Molecular Methods in Soft Tissue Sarcomas: From Diagnostics to Theragnostics

Soft tissue sarcomas (STSs) are a diverse group of malignant tumors derived from mesenchymal tissues [...].

Soft tissue sarcomas at the single-cell and spatial resolution: new markers and targets

Soft tissue sarcomas (STS) are heterogeneous and aggressive tumors, originating in connective tissues embryologically derived from the mesenchyme. Due to their rarity, crucial information about their biology is still lacking. In recent years, single-cell and spatial analyses have opened up new horizons in oncology, leading to the possibility of characterizing the internal architecture of the tumor at the single-cell and spatial levels. This review summarizes the first results acquired through these revolutionary methods for different types of STS. We discuss tumor cell populations and their evolution, interactions between tumor cells and the microenvironment, new prognostic markers, and clinically important targets. Finally, we examine the challenges presented by the single-cell and spatial omics of STS and the future perspectives in this field.

Investigating intra-tumoural heterogeneity and microenvironment diversity in primary cardiac angiosarcoma through single-cell RNA sequencing

BACKGROUND

Primary cardiac angiosarcoma (PCAS) is a rare and aggressive heart tumour with limited treatment options and a poor prognosis. Understanding cellular heterogeneity and tumour microenvironment (TME) is crucial for the development of effective therapies. Here, we investigated the intratumoural heterogeneity and TME diversity of PCAS using single-cell RNA sequencing (scRNA-seq).

METHODS

We performed scRNA-seq analysis on tumour samples from four patients with PCAS, supplemented with multicolour immunohistochemistry for identification. We used scRNA-seq data from five normal cardiac tissue samples downloaded from public databases for comparative analyses. Bioinformatic analyses, including Cell Ranger, Seurat, Monocle2, hdWGCNA, SCENIC and NicheNet, were utilized to identify distinct cell populations, transcriptional patterns, and co-regulating gene modules.

RESULTS

Our analysis revealed significant intratumoural heterogeneity in PCAS driven by diverse biological processes such as protein synthesis, degradation, and RIG-I signalling inhibition. The SCENIC analysis identified three primary transcription factors' clusters (CEBPB, MYC and TAL1). T-cell subset analysis showed exhausted antigen-specific T-cells, complicating the efficacy of immune checkpoint blockade. Furthermore, we observed suppressive macrophages (SPP1+ and OLR1+) and reduced mitochondrial gene MT-RNR2 (MTRNR2L12) expression in TME-infiltrating cells, indicating impaired mitochondrial function.

CONCLUSION

This study elucidates the complex cellular landscape and immune microenvironment of PCAS, highlighting potential molecular targets for the development of novel therapies. These findings underscore the importance of a multifaceted therapeutic approach for addressing the challenges posed by PCAS's heterogeneity and immune evasion.

KEY POINTS

Insights into the heterogeneity and transcriptional patterns of sarcoma cells may explain the challenges in treating primary cardiac angiosarcoma (PCAS) using the current therapeutic modalities. Characterization of the immune microenvironment revealed significant immunosuppression mediated by specific myeloid cell populations (SPP1+ and OLR1+ macrophages). Identification of mitochondrial dysfunction in immune cells within the PCAS microenvironment, particularly the notable downregulation of the MTRNR2L12 protein, suggests a new avenue for therapeutic targeting.

FGF23 Expression Is a Promising Immunohistochemical Diagnostic Marker for Undifferentiated Pleomorphic Sarcoma of Bone (UPSb)

Background: Undifferentiated pleomorphic sarcoma of bone (UPSb) is a rare primary bone sarcoma that lacks a specific line of differentiation. Distinguishing between UPSb and other malignant bone sarcomas, including dedifferentiated chondrosarcoma and osteosarcoma, is challenging due to their overlapping features. We have previously identified that UPSb tumours have elevated mRNA levels of Fibroblast Growth Factor 23 (FGF23) transcripts compared to other sarcomas including osteosarcoma. In the present study, we evaluated the specificity and practicality of FGF23 immunoreactivity as a specific diagnostic tool to differentiate UPSb tumours from osteosarcomas and dedifferentiated chondrosarcomas. Methods: A total of 10 UPSb, 10 osteosarcoma, and 10 dedifferentiated chondrosarcoma cases (all high-grade), were retrieved and immunohistochemistry for FGF23 was performed. Results: FGF23 protein was expressed at high levels in 80-90% of undifferentiated pleomorphic sarcoma of the bone cases, whereas it was expressed at significantly lower levels in dedifferentiated chondrosarcoma and osteosarcoma cases. A semiquantitative analysis, considering the intensity of immunoreactivity, confirmed significantly elevated FGF23 expression levels in UPSb tissues compared to those observed in osteosarcoma and dedifferentiated chondrosarcoma tissues. Conclusions: The results we present here suggest that FGF23 immunohistochemistry may be a useful tool to aid in differentiating UPSb from morphologically similar malignant bone sarcomas, especially in situations where sampling is restricted and there is limited clinical information available.