Clinical implications and molecular features of extracellular matrix networks in soft tissue sarcomas.

PURPOSE: The landscape of extracellular matrix (ECM) alterations in soft tissue sarcomas (STS) remains poorly characterised. We aimed to investigate the tumour ECM and adhesion signalling networks present in STS and their clinical implications. EXPERIMENTAL DESIGN: Proteomic and clinical data from 321 patients across 11 histological subtypes were analysed to define ECM and integrin adhesion networks. Subgroup analysis was performed in leiomyosarcomas (LMS), dedifferentiated liposarcomas (DDLPS) and undifferentiated pleiomorphic sarcomas (UPS). RESULTS: This analysis defined subtype-specific ECM profiles including enrichment of basement membrane proteins in LMS and ECM proteases in UPS. Across the cohort, we identified three distinct co-regulated ECM networks which are associated with tumour malignancy grade and histological subtype. Comparative analysis of LMS cell line and patient proteomic data identified the LCP1 cytoskeletal protein as a prognostic factor in LMS. Characterisation of ECM network events in DDLPS revealed three subtypes with distinct oncogenic signalling pathways and survival outcomes. Evaluation of the DDLPS subtype with the poorest prognosis nominates ECM remodelling proteins as candidate anti-stromal therapeutic targets. Finally, we define a proteoglycan signature which is an independent prognostic factor for overall survival in DDLPS and UPS. CONCLUSIONS: STS comprise heterogeneous ECM signalling networks and matrix-specific features have utility for risk stratification and therapy selection which could in future guide precision medicine in these rare cancers.

The proteomic landscape of soft tissue sarcomas.

Soft tissue sarcomas (STS) are rare and diverse mesenchymal cancers with limited treatment options. Here we undertake comprehensive proteomic profiling of tumour specimens from 321 STS patients representing 11 histological subtypes. Within leiomyosarcomas, we identify three proteomic subtypes with distinct myogenesis and immune features, anatomical site distribution and survival outcomes. Characterisation of undifferentiated pleomorphic sarcomas and dedifferentiated liposarcomas with low infiltrating CD3 + T-lymphocyte levels nominates the complement cascade as a candidate immunotherapeutic target. Comparative analysis of proteomic and transcriptomic profiles highlights the proteomic-specific features for optimal risk stratification in angiosarcomas. Finally, we define functional signatures termed Sarcoma Proteomic Modules which transcend histological subtype classification and show that a vesicle transport protein signature is an independent prognostic factor for distant metastasis. Our study highlights the utility of proteomics for identifying molecular subgroups with implications for risk stratification and therapy selection and provides a rich resource for future sarcoma research.

Current Status and Future Directions of Immunotherapies in Soft Tissue Sarcomas.

Immunotherapy in soft tissue sarcoma (STS) has experienced a surge of interest in the past decade, contributing to an expanding number of therapeutic options for this extremely heterogenous group of rare malignancies. Immune checkpoint inhibitors (CPIs) targeting the PD-1 and CTLA-4 axes have demonstrated promising responses in a select number of STS subtypes, including rarer subtypes, such as alveolar soft part sarcoma, SWI/SNF-deficient sarcomas, clear cell sarcoma, and angiosarcoma. Multiple pan-subtype sarcoma trials have facilitated the study of possible predictive biomarkers of the CPI response. It has also become apparent that certain therapies, when combined with CPIs, can enhance response rates, although the specific mechanisms of this possible synergy remain unconfirmed in STS. In addition to CPIs, several other immune targeting agents, including anti-tumour-associated macrophage and antigen-directed therapies, are now under assessment in STS with promising efficacy in some subtypes. In this article, we review the state of the art in immunotherapy in STS, highlighting the pre-clinical and clinical data available for this promising therapeutic strategy.

Olaratumab in soft tissue sarcoma - Current status and future perspectives.

Recent randomised phase II trial data have indicated that the addition of olaratumab, a novel monoclonal antibody against platelet-derived growth factor receptor alpha (PDGFRα), to doxorubicin confers an unprecedented improvement in overall survival to patients with anthracycline-naïve advanced soft tissue sarcoma. However, this result was disproportionate with progression-free survival and response rate, and consequently there are unanswered questions regarding the precise mechanism of action of olaratumab. While preclinical data show that olaratumab specifically inhibits PDGFRα-mediated oncogenic signalling with attendant anti-tumour effects, a lack of correlation between pharmacodynamics markers of PDGFRα inhibition and clinical benefit from olaratumab suggest other mechanisms beyond modulation of downstream PDGFRα molecular pathways. Proposed mechanisms of olaratumab activity include engagement of anti-tumour immune responses and alterations of the tumour stroma, but these require further evaluation. Meanwhile, the drug-specific contribution of cytotoxic agents to olaratumab-containing combinations has yet to be characterised. Ongoing and future preclinical and translational studies, coupled with the anticipated results of a phase III trial that has completed enrolment, should provide greater insight into the efficacy and mode of action of olaratumab in soft tissue sarcomas.

Phase III Soft Tissue Sarcoma Trials: Success or Failure?

OPINION STATEMENT: Two recently reported phase III randomised control trials (RCTs) have resulted in the registration of two new systemic therapies for advanced soft tissue sarcoma. Both of these trials' designs were informed by phase II data that guided the selection of sensitive STS diagnoses, enabling the demonstration of benefit in certain subtypes. A number of other phase III trials reported in the last 18 months have seemingly fit into a recurrent pattern of failure-promising efficacy signals in earlier phase studies being lost in the survival follow-up of large, highly heterogeneous cohorts. Greater effort is needed to identify histological and molecularly defined subgroups associated with differential treatment response in order to avoid the tremendous disappointment and loss of resources associated with a failed phase III trial. Additionally, improvements in available treatment of advanced STS have underpinned a prolongation in overall survival (OS). Consequently, surrogate efficacy endpoints are of increasing importance to STS drug trials. Whilst progression-free survival (PFS) should arguably replace overall survival as the primary endpoint of choice in first-line studies, more work is required to provide definitive validation of surrogacy, as well as developing more sophisticated techniques of assessing radiological response and expanding the inclusion of quality-of-life-related endpoints.