Beyond the Driver Mutation: Immunotherapies in Gastrointestinal Stromal Tumors

PTGR1-mediated immune evasion mechanisms in late-stage triple-negative breast cancer: mechanisms of M2 macrophage infiltration and CD8+ T cell suppression

Triple-negative breast cancer (TNBC) is a heterogeneous disease characterized by metabolic dysregulation. Tumor cell immune escape plays an indispensable role in the development of TNBC tumors. Furthermore, in the abstract, we explicitly mention the techniques used and enhance the clarity and impact of our findings. "Based on bioinformatics analysis results, we utilized CRISPR/Cas9 technology to knockout the target gene and established a mouse model of breast cancer. Through experiments such as CCK8, scratch assay, and Transwell assay, we further investigated the impact of target gene knockout on the malignant behavior of tumor cells. Subsequently, we conducted immunohistochemistry and Western Blot experiments to study the expression of macrophage polarization and infiltration-related markers and evaluate the effect of the target gene on macrophage polarization. Next, through co-culture experiments, we simulated the tumor microenvironment and used immunohistochemistry staining to observe and analyze the distribution and activation status of M2 macrophages and CD8+ T cells in the co-culture system. We validated in vivo experiments the molecular mechanism by which the target gene regulates immune cell impact on TNBC progression.

Advances in immunotherapy of M2 macrophages and gastrointestinal stromal tumor

Gastrointestinal stromal tumors (GIST) are the most common mesenchymal-derived tumors of the GI tract. They can occur throughout the GI tract, and the survival time of some patients can be improved by first-line targeted therapy with imatinib. However, there are some limitations with imatinib treatment. Immunotherapy for GIST has attracted much attention in recent years, and as one of the most abundant cells in the GIST microenvironment, M2 macrophages play an important role in disease progression. They have unique anti-inflammatory and pro-tumorigenic effects and are one target for immunotherapy. This review summarizes the connection between different factors and the programmed death receptor-1/programmed death ligand-1 pathway and M2 macrophages to reactivate or enhance anti-tumor immunity and improve imatinib efficacy, and to provide new ideas for GIST immunotherapy.

Macrophages and tertiary lymphoid structures as indicators of prognosis and therapeutic response in cancer patients

Tertiary lymphoid structures (TLS) can reflect cancer prognosis and clinical outcomes in various tumour tissues. Tumour-associated macrophages (TAMs) are indispensable components of the tumour microenvironment and play crucial roles in tumour development and immunotherapy. TAMs are associated with TLS induction via the modulation of the T cell response, which is a major component of the TLS. Despite their important roles in cancer immunology, the subtypes of TAMs that influence TLS and their correlation with prognosis are not completely understood. Here, we provide novel insights into the role of TAMs in regulating TLS formation. Furthermore, we discuss the prognostic value of these TAM subtypes and TLS, as well as the current antitumour therapies for inducing TLS. This study highlights an entirely new field of TLS regulation that may lead to the development of an innovative perspective on immunotherapy for cancer treatment.

Tertiary lymphoid structural heterogeneity determines tumour immunity and prospects for clinical application

Tertiary lymphoid structures (TLS) are clusters of immune cells that resemble and function similarly to secondary lymphoid organs (SLOs). While TLS is generally associated with an anti-tumour immune response in most cancer types, it has also been observed to act as a pro-tumour immune response. The heterogeneity of TLS function is largely determined by the composition of tumour-infiltrating lymphocytes (TILs) and the balance of cell subsets within the tumour-associated TLS (TA-TLS). TA-TLS of varying maturity, density, and location may have opposing effects on tumour immunity. Higher maturity and/or higher density TLS are often associated with favorable clinical outcomes and immunotherapeutic response, mainly due to crosstalk between different proportions of immune cell subpopulations in TA-TLS. Therefore, TLS can be used as a marker to predict the efficacy of immunotherapy in immune checkpoint blockade (ICB). Developing efficient imaging and induction methods to study TA-TLS is crucial for enhancing anti-tumour immunity. The integration of imaging techniques with biological materials, including nanoprobes and hydrogels, alongside artificial intelligence (AI), enables non-invasive in vivo visualization of TLS. In this review, we explore the dynamic interactions among T and B cell subpopulations of varying phenotypes that contribute to the structural and functional diversity of TLS, examining both existing and emerging techniques for TLS imaging and induction, focusing on cancer immunotherapies and biomaterials. We also highlight novel therapeutic approaches of TLS that are being explored with the aim of increasing ICB treatment efficacy and predicting prognosis.

Deciphering the tumor immune microenvironment of imatinib-resistance in advanced gastrointestinal stromal tumors at single-cell resolution

The heterogeneous nature of tumors presents a considerable obstacle in addressing imatinib resistance in advanced cases of gastrointestinal stromal tumors (GIST). To address this issue, we conducted single-cell RNA-sequencing in primary tumors as well as peritoneal and liver metastases from patients diagnosed with locally advanced or advanced GIST. Single-cell transcriptomic signatures of tumor microenvironment (TME) were analyzed. Immunohistochemistry and multiplex immunofluorescence staining were used to further validate it. This analysis revealed unique tumor evolutionary patterns, transcriptome features, dynamic cell-state changes, and different metabolic reprogramming. The findings indicate that in imatinib-resistant TME, tumor cells with activated immune and cytokine-mediated immune responses interacted with a higher proportion of Treg cells via the TIGIT-NECTIN2 axis. Future immunotherapeutic strategies targeting Treg may provide new directions for the treatment of imatinib-resistant patients. In addition, IDO1+ dendritic cells (DC) were highly enriched in imatinib-resistant TME, interacting with various myeloid cells via the BTLA-TNFRSF14 axis, while the interaction was not significant in imatinib-sensitive TME. Our study highlights the transcriptional heterogeneity and distinct immunosuppressive microenvironment of advanced GIST, which provides novel therapeutic strategies and innovative immunotherapeutic agents for imatinib resistance.

KIT mutations and expression: current knowledge and new insights for overcoming IM resistance in GIST

Gastrointestinal stromal tumor (GIST) is the most common sarcoma located in gastrointestinal tract and derived from the interstitial cell of Cajal (ICC) lineage. Both ICC and GIST cells highly rely on KIT signal pathway. Clinically, about 80-90% of treatment-naive GIST patients harbor primary KIT mutations, and special KIT-targeted TKI, imatinib (IM) showing dramatic efficacy but resistance invariably occur, 90% of them was due to the second resistance mutations emerging within the KIT gene. Although there are multiple variants of KIT mutant which did not show complete uniform biologic characteristics, most of them have high KIT expression level. Notably, the high expression level of KIT gene is not correlated to its gene amplification. Recently, accumulating evidences strongly indicated that the gene coding, epigenetic regulation, and pre- or post- protein translation of KIT mutants in GIST were quite different from that of wild type (WT) KIT. In this review, we elucidate the biologic mechanism of KIT variants and update the underlying mechanism of the expression of KIT gene, which are exclusively regulated in GIST, providing a promising yet evidence-based therapeutic landscape and possible target for the conquer of IM resistance. Video Abstract.

Unexpected reaction of "wild-type" gastrointestinal stromal tumor to imatinib: case report and literature review

Background

Most of gastrointestinal stromal tumors (GISTs) are driven by mutations in the KIT/PDGFRA genes and can benefit from TKIs treatment. However, a small subset of GIST (10%-15%) are called "wild-type" GISTs due to the lack of these mutations. Theoretically, they would not benefit from TKIs treatment and may even develop resistance. Therefore, this unexpected response may challenge inherent perceptions. Herein, we present a case of giant wild-type GIST exhibiting an unexpected response to imatinib(IM), followed by laparoscopic surgical resection. Subsequently, potential underlying mechanisms are discussed.

Case description

This case describes a 57-year-old man who presented with abdominal pain for two weeks. CT revealed a massive lesion near the splenic hilum along the greater curvature of the stomach, concurrently involving the splenic hilar vessels and surrounding lymph nodes. Ultrasound-guided fine needle aspiration biopsy confirmed it is a mesenchymal spindle cell tumor,GIST. Due to the enormous volume and local invasion, neoadjuvant chemotherapy was initially considered. After 6 months of IM 400 mg/d, CT imaging revealed marked changes in tumor heterogeneity and a significant reduction in volume. Subsequently, laparoscopic surgical resection was performed. Postoperative pathological examination, immunohistochemistry, and genetic testing collectively confirmed it is a wild-type GIST.The patient recovered well and was discharged on the 6th day after surgery, with continued oral IM(400 mg/d) after discharge. No recurrence was observed during follow-up until the publication of this report.

Conclusion

This unexpected response suggests that wild-type GISTs may benefit from TKIs treatment, and the potential mechanisms warrant further investigation. Additionally, true wild-type GIST may not be discerned due to current limitations of Next-Generation Sequencing(NGS). Therefore, for advanced/high-risk GIST, additional genetic analysis can be performed after negative NGS results.

Advances in Drug Therapy for Gastrointestinal Stromal Tumour

INTRODUCTION

Gastrointestinal stromal tumour (GIST) is a common gastrointestinal sarcoma located in the stromal cells of the digestive tract, and molecular studies have revealed the pathogenesis of mutations in KIT and PDGFRA genes. Since imatinib opened the era of targeted therapy for GIST, tyrosine kinase inhibitors (TKIs) that can treat GIST have been developed successively. However, the lack of new drugs with satisfactory therapeutic standards has made addressing resistance a significant challenge for TKIs in the face of the resistance to first-line and second-line drugs. Therefore, we need to find as many drugs and new treatments that block mutated genes as possible.

METHODS

We conducted a comprehensive collection of literature using databases, integrated and analysed the selected literature based on keywords and the comprehensive nature of the articles, and finally wrote articles based on the content of the studies.

RESULTS

In this article, we first briefly explained the relationship between GIST and KIT/ PDGFRα and then introduced the related drug treatment. The research progress of TKIs was analyzed according to the resistance of the drugs.

CONCLUSION

This article describes the research progress of some TKIs and briefly introduces the currently approved TKIs and some drugs under investigation that may have better therapeutic effects, hoping to provide clues to the research of new drugs.

Advances in immunology and immunotherapy for mesenchymal gastrointestinal cancers

Mesenchymal gastrointestinal cancers are represented by the gastrointestinal stromal tumors (GISTs) which occur throughout the whole gastrointestinal tract, and affect human health and economy globally. Curative surgical resections and tyrosine kinase inhibitors (TKIs) are the main managements for localized GISTs and recurrent/metastatic GISTs, respectively. Despite multi-lines of TKIs treatments prolonged the survival time of recurrent/metastatic GISTs by delaying the relapse and metastasis of the tumor, drug resistance developed quickly and inevitably, and became the huge obstacle for stopping disease progression. Immunotherapy, which is typically represented by immune checkpoint inhibitors (ICIs), has achieved great success in several solid tumors by reactivating the host immune system, and been proposed as an alternative choice for GIST treatment. Substantial efforts have been devoted to the research of immunology and immunotherapy for GIST, and great achievements have been made. Generally, the intratumoral immune cell level and the immune-related gene expressions are influenced by metastasis status, anatomical locations, driver gene mutations of the tumor, and modulated by imatinib therapy. Systemic inflammatory biomarkers are regarded as prognostic indicators of GIST and closely associated with its clinicopathological features. The efficacy of immunotherapy strategies for GIST has been widely explored in pre-clinical cell and mouse models and clinical experiments in human, and some patients did benefit from ICIs. This review comprehensively summarizes the up-to-date advancements of immunology, immunotherapy and research models for GIST, and provides new insights and perspectives for future studies.

Molecular Tailored Therapeutic Options for Advanced Gastrointestinal Stromal Tumors (GISTs): Current Practice and Future Perspectives

Gastrointestinal stromal tumors (GISTs) are one of the most common mesenchymal tumors characterized by different molecular alterations that lead to specific clinical presentations and behaviors. In the last twenty years, thanks to the discovery of these mutations, several new treatment options have emerged. This review provides an extensive overview of GISTs’ molecular pathways and their respective tailored therapeutic strategies. Furthermore, current treatment strategies under investigation and future perspectives are analyzed and discussed.

ADRB2 Regulates the Proliferation and Metastasis of Gastrointestinal Stromal Tumor Cells by Enhancing the ETV1-c-KIT Signaling

Background

Gastrointestinal stromal tumor (GIST) originates from a pacemaker cell, the Cajal cell. However, little is known about the cancer neuroscience in GIST. In this study, we aimed to elucidate the clinical and biological roles of adrenoceptor beta 2 (ADRB2) in GIST.

Methods

Immunohistochemistry was used to evaluate the expression of ADRB2 in GIST tissues. The biological effects of ADRB2 on GIST cell proliferation, migration, invasion, and apoptosis were explored using Cell Counting Kit -8, plate colony formation assay, transwell invasion assay, and flow cytometry. We also explored the growth and metastasis of xenograft tumors in nude mice. Western blotting was used to quantify protein expression and phosphorylation.

Results

ADRB2 is generally highly expressed in GIST. High ADRB2 expression was significantly associated with risk level, tumor size, mitotic count, and metastasis. Overexpression of ADRB2 promoted GIST cell proliferation, migration, invasion, and apoptosis, while silencing ADRB2 expression showed the opposite effects. Furthermore, we found that silencing endogenous ADRB2 inhibited GIST progression and metastasis in nude mice. ADRB2-induced ETV1 upregulation enhanced the activation of c-KIT.

Conclusion

ADRB2 plays an important role in the proliferation and metastasis of GIST and is expected to be a potential target for the treatment of GIST.

Exploring the Dynamic Crosstalk between the Immune System and Genetics in Gastrointestinal Stromal Tumors

Gastrointestinal Stromal Tumors (GISTs) represent a paradigmatic model of oncogene addiction. Despite the well-known impact of the mutational status on clinical outcomes, we need to expand our knowledge to other factors that influence behavior heterogeneity in GIST patients. A growing body of studies has revealed that the tumor microenvironment (TME), mostly populated by tumor-associated macrophages (TAMs) and lymphocytes (TILs), and stromal differentiation (SD) have a significant impact on prognosis and response to treatment. Interestingly, even though the current knowledge of the role of immune response in this setting is still limited, recent pre-clinical and clinical data have highlighted the relevance of the TME in GISTs, with possible implications for clinical practice in the near future. Moreover, the expression of immune checkpoints, such as PD-L1, PD-1, and CTLA-4, and their relationship to the clinical phenotype in GIST are emerging as potential prognostic biomarkers. Looking forward, these variables related to the underlying tumoral microenvironment in GIST, though limited to still-ongoing trials, might lead to the potential use of immunotherapy, alone or in combination with targeted therapy, in advanced TKI-refractory GISTs. This review aims to deepen understanding of the potential link between mutational status and the immune microenvironment in GIST.

The Prognostic Value of Plasma Programmed Death Protein-1 (PD-1) and Programmed Death-Ligand 1 (PD-L1) in Patients with Gastrointestinal Stromal Tumor

BACKGROUND

This study investigates the prognostic value of plasma Programmed Death Protein-1 (PD-1) and Programmed Death-Ligand 1 (PD-L1) concentrations in patients with Gastrointestinal Stromal Tumor (GIST).

METHODS

Patients with GIST were included (n = 157) from the two Danish sarcoma centers, independent of disease- and treatment status. The patients were divided into three subgroups; 1: patients with localized disease who underwent radical surgery; 2: patients with local, locally advanced, or metastatic disease; and 3: patients without measurable disease who had undergone radical surgery. Sensitive electrochemiluminescence immune-assays were used to determine PD-1 and PD-L1 concentration in plasma samples. The primary endpoint was the PFS.

RESULTS

No patients progressed in group 1 (n = 15), 34 progressed in group 2 (n = 122), and three progressed in group 3 (n = 20). Significantly higher plasma concentrations of PD-1 (p = 0.0023) and PD-L1 (0.012) were found in patients in group 2 compared to PD-1/PD-L1 levels in postoperative plasma samples from patient group 1. Patients with active GIST having a plasma concentration of PD-L1 above the cutoff (225 pg/mL) had a significantly poorer prognosis compared to patients with plasma PD-L1 concentration below the cutoff.

CONCLUSIONS

Plasma PD-L1 shows potential as a prognostic biomarker in patients with GIST and should be further evaluated.

miRNA Expression May Have Implications for Immunotherapy in PDGFRA Mutant GISTs

Gastrointestinal stromal tumors (GISTs) harboring mutations in the PDGFRA gene occur in only about 5-7% of patients. The most common PDGFRA mutation is exon 18 D842V, which is correlated with specific clinico-pathological features compared to the other PDGFRA mutated GISTs. Herein, we present a miRNA expression profile comparison of PDGFRA D842V mutant GISTs and PDGFRA with mutations other than D842V (non-D842V). miRNA expression profiling was carried out on 10 patients using a TLDA miRNA array. Then, miRNA expression was followed by bioinformatic analysis aimed at evaluating differential expression, pathway enrichment, and miRNA-mRNA networks. We highlighted 24 differentially expressed miRNAs between D842V and non-D842V GIST patients. Pathway enrichment analysis showed that deregulated miRNAs targeted genes that are mainly involved in the immune response pathways. The miRNA-mRNA networks highlighted a signature of miRNAs/mRNA that could explain the indolent behavior of the D842V mutated GIST. The results highlighted a different miRNA fingerprint in PDGFRA D842V GISTs compared to non-D842Vmutated patients, which could explain the different biological behavior of this GIST subset.

Characterization of PDL1 enhanced siRNA/albumin liposome for effective therapeutic function in lung cancer

PURPOSE

The applications of liposomes are limited due to poor structural stability and short drug circulation time. This study aims to build an albumin-based liposomal delivery system to provide strategies for tumor specificity, efficient gene delivery and effective release of albumin liposomes.

METHODS

In this study, siRNA loaded PDL1-targeted albumin liposome was constructed for the treatment of lung cancer and its function was evaluated. Physical parameters such as particle size, potential and infrared spectrum were detected and microscopic morphology was observed by electron microscopy to detect the binding and uptake capacity of albumin liposome with cells. The optimal preparation process and binding ratio of PDL1-targeted albumin liposome/siRNA complex were determined.

RESULTS

The constructed siRNA loaded PDL1-targeted albumin liposomes has low toxicity, high loading rate and tumor cell targeted gene therapy ability. Moreover, it increased T cell activation and down-regulated siRNA expression, effectively realizing the inhibition of lung cancer cells.

CONCLUSION

The results showed that the PDL1-targeted albumin liposome could be used as a high efficient delivery vector of siRNA, and was a high efficient and safe nano vector for tumor targeted gene therapy.

Correlation between PD-1/PD-L1 expression and polarization in tumor-associated macrophages: A key player in tumor immunotherapy

Tumor immunotherapy, such as PD-1/PD-L1 blockade, has shown promising clinical efficacy in patients with various types of tumors. However, the response to PD-1/PD-L1 blockade in a majority of malignancies is limited, indicating an urgent need for a deeper understanding of the mechanisms of PD-1/PD-L1 axis-mediated tumor tolerance. As the most abundant immune cells in the tumor stroma, macrophages display multiple phenotypes and functions in response to the stimuli of the tumor microenvironment. PD-1/PD-L1 has been demonstrated to be highly expressed in tumor-associated macrophages (TAMs), and TAM polarization has been shown to be important during tumor progression. In this review, we outline the relationship between TAM PD-1/PD-L1 expression and polarizations, summarize the involvement of M2 TAMs in PD-1/PD-L1-mediated T-cell exhaustion, and discuss improved approaches for overcoming PD-1/PD-L1 blockade resistance by inducing M2/M1 switching of TAMs.

Tertiary Lymphatic Structures in Primary Hepatic Carcinoma: Controversy Cannot Overshadow Hope

Tertiary lymphoid structures (TLSs) are organized aggregates of immune cells found in the tumor microenvironment. TLS can influence primary hepatic carcinoma (PHC) occurrence and have an active role in cancer. TLS can promote or inhibit the growth of PHC depending on their location, and although available findings are controversial, they suggest that TLS have a protective role in PHC tissues and a non-protective role in paracancerous tissues. In addition, the cellular composition of TLS can also influence the outcome of PHC. As an immunity marker, TLS can act as a marker of immunotherapy to predict its effect and help to identify patients who will respond well to immunotherapy. Modulation of TLS formation through the use of chemokines/cytokines, immunotherapy, or induction of high endothelial vein to interfere with tumor growth has been studied extensively in PHC and other cancers. In addition, new tools such as genetic interventions, cellular crosstalk, preoperative radiotherapy, and advances in materials science have been shown to influence the prognosis of malignant tumors by modulating TLS production. These can also be used to develop PHC treatment.

Novel Hypoxia-Associated Gene Signature Depicts Tumor Immune Microenvironment and Predicts Prognosis of Colon Cancer Patients

Hypoxia, a typical hallmark of numerous tumors, indicates poor infiltration of antitumor lymphocytes, as well as facilitates the development, progression, and drug resistance of malignant cells. Here, the present research was performed to identify novel hypoxia-related molecular markers and their correlation to the tumor immune microenvironment (TIME) in colon cancer. The expression of hypoxia-related gene signature was extracted from The Cancer Genome Atlas (TCGA) COAD cohort. Based on this signature, a risk score model was constructed using the Lasso regression model. Its discrimination ability and stability were validated in another independent cohort (GSE17536) from Gene Expression Omnibus (GEO) database. Moreover, molecular biology experiments (quantitative real-time PCR and multiple immunohistochemistry) were performed to validate the results of bioinformatics analyses. Three hub genes, including PPFIA4, SERPINE1, and STC2, were chosen to build the risk score model. All of these genes were increasingly expressed in the hypoxia subgroup (HS). Compared with the normoxia subgroup (NS), HS had worse pathological features (T, N, M, and stage) and overall survival (OS), more expression of immune checkpoint molecules, poorer infiltration of some pro-inflammation immune cells (CD4⁺ T cells and CD8⁺ T cells), and enriched infiltration of M0/M2 macrophages. After the risk model was proven to be valuable and stable, a nomogram was built based on this model and some clinicopathological factors. Moreover, it had been identified that three hub genes were all increasingly expressed in hypoxic conditions by quantitative real-time PCR (qPCR). The results of multiple immunohistochemistry (mIHC) also showed that higher expression of hub genes was associated with poorer infiltration of pro-inflammation immune cells (CD8⁺ T cells and M1 macrophages) and richer infiltration of anti-inflammation immune cells (Treg cells and M2 macrophages). In conclusion, the present study uncovered the relations among hypoxia, TIME, and clinicopathological features of colon cancer. It might provide new insight and a potential therapeutic target for immunotherapy.

Improving Immunotherapy Efficacy in Soft-Tissue Sarcomas: A Biomarker Driven and Histotype Tailored Review

Anti-PD-(L)1 therapies yield a disappointing response rate of 15% across soft-tissue sarcomas, even if some subtypes benefit more than others. The proportions of TAMs and TILs in their tumor microenvironment are variable, and this heterogeneity correlates to histotype. Tumors with a richer CD8+ T cell, M1 macrophage, and CD20+ cells infiltrate have a better prognosis than those infiltrated by M0/M2 macrophages and a high immune checkpoint protein expression. PD-L1 and CD8+ infiltrate seem correlated to response to immune checkpoint inhibitors (ICI), but tertiary lymphoid structures have the best predictive value and have been validated prospectively. Trials for combination therapies are ongoing and focus on the association of ICI with chemotherapy, achieving encouraging results especially with pembrolizumab and doxorubicin at an early stage, or ICI with antiangiogenics. A synergy with oncolytic viruses is seen and intratumoral talimogene laherpavec yields an impressive 35% ORR when associated to pembrolizumab. Adoptive cellular therapies are also of great interest in tumors with a high expression of cancer-testis antigens (CTA), such as synovial sarcomas or myxoid round cell liposarcomas with an ORR ranging from 20 to 50%. It seems crucial to adapt the design of clinical trials to histology. Leiomyosarcomas are characterized by complex genomics but are poorly infiltrated by immune cells and do not benefit from ICI. They should be tested with PIK3CA/AKT inhibition, IDO blockade, or treatments aiming at increasing antigenicity (radiotherapy, PARP inhibitors). DDLPS are more infiltrated and have higher PD-L1 expression, but responses to ICI remain variable across clinical studies. Combinations with MDM2 antagonists or CDK4/6 inhibitors may improve responses for DDLPS. UPS harbor the highest copy number alterations (CNA) and mutation rates, with a rich immune infiltrate containing TLS. They have a promising 15-40% ORR to ICI. Trials for ICB should focus on immune-high UPS. Association of ICI with FGFR inhibitors warrants further exploration in the immune-low group of UPS. Finally translocation-related sarcomas are heterogeneous, and although synovial sarcomas a poorly infiltrated and have a poor response rate to ICI, ASPS largely benefit from ICB monotherapy or its association with antiangiogenics agents. Targeting specific neoantigens through vaccine or adoptive cellular therapies is probably the most promising approach in synovial sarcomas.