Molecular genetics of sarcomas: applications to diagnoses and therapy

Individualized Mini-Panel Sequencing of ctDNA Allows Tumor Monitoring in Complex Karyotype Sarcomas

Soft tissue sarcomas (STS) are rare tumors of mesenchymal origin with high mortality. After curative resection, about one third of patients suffer from distant metastases. Tumor follow-up only covers a portion of recurrences and is associated with high cost and radiation burden. For metastasized STS, only limited inferences can be drawn from imaging data regarding therapy response. To date there are no established and evidence-based diagnostic biomarkers for STS due to their rarity and diversity. In a proof-of-concept study, circulating tumor DNA (ctDNA) was quantified in (n = 25) plasma samples obtained from (n = 3) patients with complex karyotype STS collected over three years. Genotyping of tumor tissue was performed by exome sequencing. Patient-individual mini-panels for targeted next-generation sequencing were designed encompassing up to 30 mutated regions of interest. Circulating free DNA (cfDNA) was purified from plasma and ctDNA quantified therein. ctDNA values were correlated with clinical parameters. ctDNA concentrations correlated with the tumor burden. In case of full remission, no ctDNA was detectable. Patients with a recurrence at a later stage showed low levels of ctDNA during clinical remission, indicating minimal residual disease. In active disease (primary tumor or metastatic disease), ctDNA was highly elevated. We observed direct response to treatment, with a ctDNA decline after tumor resections, radiotherapy, and chemotherapy. Quantification of ctDNA allows for the early detection of recurrence or metastases and can be used to monitor treatment response in STS. Therapeutic decisions can be made earlier, such as the continuation of a targeted adjuvant therapy or the implementation of extended imaging to detect recurrences. In metastatic disease, therapy can be adjusted promptly in case of no response. These advantages may lead to a survival benefit for patients in the future.

Therapeutic potential of TAS-115 via c-MET and PDGFRα signal inhibition for synovial sarcoma

Background

The prognosis of synovial sarcoma (SS), an aggressive soft tissue sarcoma, remains poor. We previously reported that c-MET or platelet-derived growth factor receptor α (PDGFRα) signalling pathway is related to SS progression based upon the findings of phospho-receptor tyrosine kinase (RTK) arrays. TAS-115 is a novel c-MET/ vascular endothelial growth factor receptor-targeting tyrosine kinase inhibitor that has been shown to inhibit multiple RTKs. Here we aimed to investigate the therapeutic potential of TAS-115 against SS.

Methods

We first evaluated which signalling pathway was relevant to the viability of three human SS cell lines: Yamato-SS, SYO-1 and HS-SY-II. Next, we assessed the anticancer activity and mechanism of action of TAS-115 in these SS cell lines. Finally, we compared the ability of TAS-115 to inhibit c-MET and PDGFRα phosphorylation with that of pazopanib.

Results

We classified the SS cell lines as c-MET-dependent or PDGFRα-dependent based upon the differences in the signalling pathway relevant for growth and/or survival. We also found that c-MET and PDGFRα were the primary activators of both phosphatidylinositol 3-kinase/AKT and mitogen-activated protein kinase pathways in c-MET-dependent and PDGFRα-dependent SS cells, respectively. TAS-115 treatment blocked the phosphorylation of PDGFRα as well as that of c-MET and their downstream effectors, leading to marked growth inhibition in both types of SS cell lines in in vitro and in vivo studies. Furthermore, PDGFRα phosphorylation, on at least four representative autophosphorylation sites, was impeded by TAS-115 equivalently to pazopanib.

Conclusions

These experimental results have demonstrated the significance of c-MET and PDGFRα signalling for growth and/or survival of SS tumours. TAS-115 monotherapy may benefit SS patients whose tumours are dependent upon either c-MET or PDGFRα signalling by functioning as a multiple tyrosine kinase inhibitor to suppress c-MET as well as PDGFRα pathways.

Electronic supplementary material

The online version of this article (doi:10.1186/s12885-017-3324-3) contains supplementary material, which is available to authorized users.

Functional and therapeutic relevance of hepatocyte growth factor/c-MET signaling in synovial sarcoma

Synovial sarcoma (SS) is an aggressive soft tissue sarcoma with a poor prognosis and, thus, novel therapeutic strategies for SS are urgently required. In the present study, we investigated the functional and therapeutic relevance of hepatocyte growth factor (HGF)/c‐MET signaling in SS. Both HGF and c‐MET were highly expressed in Yamato‐SS cells, resulting in activation of c‐MET and its downstream AKT and extracellular signal‐regulated kinase signaling pathways, whereas c‐MET was expressed but not activated in SYO‐1 or HS‐SY‐II cells. c‐MET‐activated Yamato‐SS cells showed higher anchorage‐independent growth ability and less sensitivity to chemotherapeutic agents than did c‐MET‐inactivated SYO‐1 or HS‐SY‐II cells. INC280, a selective c‐MET inhibitor, inhibited growth of Yamato‐SS cells both in vitro and in vivo but not that of SYO‐1 or HS‐SY‐II cells. INC280 induced cell cycle arrest and apoptosis, and blocked phosphorylation of c‐MET and its downstream effectors in Yamato‐SS cells. Co‐expression of HGF and c‐MET in SS clinical samples correlated with a poor prognosis in patients with SS. Taken together, activation of HGF/c‐MET signaling in an autocrine fashion leads to an aggressive phenotype in SS and targeting of this signaling exerts superior antitumor effects on c‐MET‐activated SS. HGF/c‐MET expression status is a potential biomarker for identification of SS patients with a worse prognosis who can benefit from c‐MET inhibitors.

Translational research in diagnosis and management of soft tissue tumours

Finding a soft tissue mass in the superficial regions is a common event in daily clinical practice. Correct management of the diagnostic process is crucial to avoid blunders. Diagnosis is posed by pathology, although both imaging and a better understanding of the cellular and molecular mechanisms play an important a role in the characterization, staging and follow-up of soft tissue masses. Cellular and molecular mechanisms can explain either the development of chemo-resistance and the underlying pre- and post-surgery metastasis formation. These are mandatory to improve prognosis and unveil novel parameters predicting therapeutic response. Imaging mainly involves ultrasound and MR and is fundamental not only in diagnosis but also in the first step of therapy: the biopsy. Novel imaging techniques like Ultrasound Elastosonography, Dynamic Contrast-Enhanced MR imaging (DCE), Diffusion Weighted MR imaging (DWI) and MR Spectroscopy (MRS) are discussed. This paper aims at reviewing and discussing pathological methods and imaging in the diagnosis of soft tissue masses underscoring that the most appropriate treatment depends on advanced molecular and radiological studies.

The fusion protein SS18-SSX1 employs core Wnt pathway transcription factors to induce a partial Wnt signature in synovial sarcoma

Expression of the SS18/SYT-SSX fusion protein is believed to underlie the pathogenesis of synovial sarcoma (SS). Recent evidence suggests that deregulation of the Wnt pathway may play an important role in SS but the mechanisms whereby SS18-SSX might affect Wnt signaling remain to be elucidated. Here, we show that SS18/SSX tightly regulates the elevated expression of the key Wnt target AXIN2 in primary SS. SS18-SSX is shown to interact with TCF/LEF, TLE and HDAC but not β-catenin in vivo and to induce Wnt target gene expression by forming a complex containing promoter-bound TCF/LEF and HDAC but lacking β-catenin. Our observations provide a tumor-specific mechanistic basis for Wnt target gene induction in SS that can occur in the absence of Wnt ligand stimulation.

Pancreatic desmoid-type fibromatosis with beta-catenin gene mutation-Report of a case and review of the literature

We experienced a rare case of pancreatic desmoid-type fibromatosis (DTF) in a 75-year-old Japanese woman. She was asymptomatic but routine examination including ultrasonography revealed a mass in the abdomen. For precise examination, she was referred to the regional hospital. Computed tomography showed that the mass was protruding anteriorly from the left-sided pancreas. Because of the enlargement of the mass lesion, distal pancreatectomy with splenectomy was performed after about 3 months. Macroscopically, the mass was encapsulated and approximately 8cm in diameter. Histological examination revealed that spindle or blunt stellate cells were proliferating in parallel or storiform fashion with myxoid and fibrous background. The tumor cells did not show prominent atypia and mitoses were rarely seen, suggesting that the tumor was low grade or borderline. Immunohistochemistry showed obvious nuclear staining of beta-catenin. Furthermore, analysis of beta-catenin gene revealed that the tumor had a typical missense mutation of threonine to alanine at colon 41 (T41A) in exon 3. These findings confirmed the pathological diagnosis of DTF of the pancreas. To the best of our knowledge, 18 cases of pancreatic DTF have been reported in the English literature and beta-catenin gene mutation had been examined in only one case among them. Thus, our case is the 19th pancreatic DTF and the second case with confirmed beta-catenin gene mutation.

Regulated lysosomal exocytosis mediates cancer progression

Understanding how tumor cells transition to an invasive and drug-resistant phenotype is central to cancer biology, but the mechanisms underlying this transition remain unclear. We show that sarcomas gain these malignant traits by inducing lysosomal exocytosis, a ubiquitous physiological process. During lysosomal exocytosis, the movement of exocytic lysosomes along the cytoskeleton and their docking at the plasma membrane involve LAMP1, a sialylated membrane glycoprotein and target of the sialidase NEU1. Cleavage of LAMP1 sialic acids by NEU1 limits the extent of lysosomal exocytosis. We found that by down-regulation of NEU1 and accumulation of oversialylated LAMP1, tumor cells exacerbate lysosomal exocytosis of soluble hydrolases and exosomes. This facilitates matrix invasion and propagation of invasive signals, and purging of lysosomotropic chemotherapeutics. In Arf (-⁄-) mice, Neu1 haploinsufficiency fostered the development of invasive, pleomorphic sarcomas, expressing epithelial and mesenchymal markers, and lysosomal exocytosis effectors, LAMP1 and Myosin-11. These features are analogous to those of metastatic, pleomorphic human sarcomas, where low NEU1 levels correlate with high expression of lysosomal exocytosis markers. In a therapeutic proof of principle, we demonstrate that inhibiting lysosomal exocytosis reversed invasiveness and chemoresistance in aggressive sarcoma cells. Thus, we reveal that this unconventional, lysosome-regulated pathway plays a primary role in tumor progression and chemoresistance.

RGS16, a novel p53 and pRb cross-talk candidate inhibits migration and invasion of pancreatic cancer cells

Data collected since the discovery of p53 and pRb/RB1 suggests these tumor suppressors cooperate to inhibit tumor progression. Patients who have mutations in both p53 and RB1 genes have increased tumor reoccurrence and decreased survival compared to patients with only one tumor suppressor gene inactivated. It remains unclear how p53 and pRb cooperate toward inhibiting tumorigenesis. Using RNA expression profiling we identified 179 p53 and pRb cross-talk candidates in normal lung fibroblasts (WI38) cells exogenously coexpressing p53 and pRb. Regulator of G protein signaling 16 (RGS16) was among the p53 and pRb cross-talk candidates and has been implicated in inhibiting activation of several oncogenic pathways associated with proliferation, migration, and invasion of cancer cells. RGS16 has been found to be downregulated in pancreatic cancer patients with metastases compared to patients without metastasis. Expression of RGS16 mRNA was decreased in the pancreatic cancer cell lines tested compared to control. Expression of RGS16 inhibited migration of the BxPC-3 and AsPC-1 but not PANC-1 cells and inhibited invasion of BxPC-3 and AsPC-1 cells with no impact on cell viability. We have identified for the first time p53 and pRb cross-talk candidates and a role for RGS16 to inhibit pancreatic cancer migration and invasion.

Recurrent LRP1-SNRNP25 and KCNMB4-CCND3 fusion genes promote tumor cell motility in human osteosarcoma

BACKGROUND

The identification of fusion genes such as SYT-SSX1/SSX2, PAX3-FOXO1, TPM3/TPM4-ALK and EWS-FLI1 in human sarcomas has provided important insight into the diagnosis and targeted therapy of sarcomas. No recurrent fusion has been reported in human osteosarcoma.

METHODS

Transcriptome sequencing was used to characterize the gene fusions and mutations in 11 human osteosarcomas.

RESULTS

Nine of 11 samples were found to harbor genetic inactivating alterations in the TP53 pathway. Two recurrent fusion genes associated with the 12q locus, LRP1-SNRNP25 and KCNMB4-CCND3, were identified and validated by RT-PCR, Sanger sequencing and fluorescence in situ hybridization, and were found to be osteosarcoma specific in a validation cohort of 240 other sarcomas. Expression of LRP1-SNRNP25 fusion gene promoted SAOS-2 osteosarcoma cell migration and invasion. Expression of KCNMB4-CCND3 fusion gene promoted SAOS-2 cell migration.

CONCLUSIONS

Our study represents the first whole transcriptome analysis of untreated human osteosarcoma. Our discovery of two osteosarcoma specific fusion genes associated with osteosarcoma cellular motility highlights the heterogeneity of osteosarcoma and provides opportunities for new treatment modalities.

Reprogramming of mesenchymal stem cells by oncogenes

Mesenchymal stem cells (MSCs) originate from embryonic mesoderm and give rise to the multiple lineages of connective tissues. Transformed MSCs develop into aggressive sarcomas, some of which are initiated by specific chromosomal translocations that generate fusion proteins with potent oncogenic properties. The sarcoma oncogenes typically prime MSCs through aberrant reprogramming. They dictate commitment to a specific lineage but prevent mature differentiation, thus locking the cells in a state of proliferative precursors. Deregulated expression of lineage-specific transcription factors and controllers of chromatin structure play a central role in MSC reprogramming and sarcoma pathogenesis. This suggests that reversing the epigenetic aberrancies created by the sarcoma oncogenes with differentiation-related reagents holds great promise as a beneficial addition to sarcoma therapies.

Metformin as an adjuvant drug against pediatric sarcomas: hypoxia limits therapeutic effects of the drug

Metformin, a well-known insulin-sensitizer commonly used for type 2 diabetes therapy, has recently emerged as potentially very attractive drug also in oncology. It is cheap, it is relatively safe and many reports have indicated effects in cancer prevention and therapy. These desirable features are particularly interesting for pediatric sarcomas, a group of rare tumors that have been shown to be dependent on IGF and insulin system for pathogenesis and progression. Metformin exerts anti-mitogenic activity in several cancer histotypes through several molecular mechanisms. In this paper, we analyzed its effects against osteosarcoma, Ewing sarcoma and rhabdomyosarcoma, the three most common pediatric sarcomas. Despite in vitro metformin gave remarkable antiproliferative and chemosensitizing effects both in sensitive and chemoresistant cells, its efficacy was not confirmed against Ewing sarcoma xenografts neither as single agent nor in combination with vincristine. This discrepancy between in vitro and in vivo effects may be due to hypoxia, a common feature of solid tumors. We provide evidences that in hypoxia conditions metformin was not able to activate AMPK and inhibit mTOR signaling, which likely prevents the inhibitory effects of metformin on tumor growth. Thus, although metformin may be considered a useful complement of conventional chemotherapy in normoxia, its therapeutic value in highly hypoxic tumors may be more limited. The impact of hypoxia should be considered when novel therapies are planned for pediatric sarcomas.

Assessment of fusion gene status in sarcomas using a custom made fusion gene microarray

Sarcomas are relatively rare malignancies and include a large number of histological subgroups. Based on morphology alone, the differential diagnoses of sarcoma subtypes can be challenging, but the identification of specific fusion genes aids correct diagnostication. The presence of individual fusion products are routinely investigated in Pathology labs. However, the methods used are time-consuming and based on prior knowledge about the expected fusion gene and often the most likely break-point. In this study, 16 sarcoma samples, representing seven different sarcoma subtypes with known fusion gene status from a diagnostic setting, were investigated using a fusion gene microarray. The microarray was designed to detect all possible exon-exon breakpoints between all known fusion genes in a single analysis. An automated scoring of the microarray data from the 38 known sarcoma-related fusion genes identified the correct fusion gene among the top-three hits in 11 of the samples. The analytical sensitivity may be further optimised, but we conclude that a sarcoma-fusion gene microarray is suitable as a time-saving screening tool to identify the majority of the correct fusion genes.

Sphere-forming cell subsets with cancer stem cell properties in human musculoskeletal sarcomas

Musculoskeletal sarcomas are aggressive malignancies often characterized by an adverse prognosis despite the use of intense multiagent chemotherapy or molecular targeted therapy in combination to surgery and radiotherapy. Stem-like cells identified within solid tumors have been recently implicated in drug resistance, metastasis and local relapse. Here, we report the identification of putative cancer stem cells (CSCs) in sarcomas using a sphere culture system. These sarcospheres, able to grow in anchorage-independent and serum-starved conditions, express the pluripotent embryonic stem cell marker genes OCT3/4, Nanog and SOX2. Expression levels of these genes were greater in sarcospheres than in the parental tumor cultures. Importantly, the isolated tumor spheres transplanted into mice were tumorigenic and capable of recapitulating the human disease. Finally, we demonstrated that low (1%) O2 conditions, reproducing those found within the tumor microenvironment, significantly increase the number and the size of sarcospheres. The sphere formation assay is, therefore, a valuable method for the isolation of putative CSCs from human sarcomas and its efficiency is improved by controlling oxygen availability. This method provides a reliable preclinical model that can be used for future studies aimed at investigating crucial aspects of sarcoma biology, such as resistance to treatments and relapse.

Breakpoint analysis of transcriptional and genomic profiles uncovers novel gene fusions spanning multiple human cancer types

Gene fusions, like BCR/ABL1 in chronic myelogenous leukemia, have long been recognized in hematologic and mesenchymal malignancies. The recent finding of gene fusions in prostate and lung cancers has motivated the search for pathogenic gene fusions in other malignancies. Here, we developed a “breakpoint analysis” pipeline to discover candidate gene fusions by tell-tale transcript level or genomic DNA copy number transitions occurring within genes. Mining data from 974 diverse cancer samples, we identified 198 candidate fusions involving annotated cancer genes. From these, we validated and further characterized novel gene fusions involving ROS1 tyrosine kinase in angiosarcoma (CEP85L/ROS1), SLC1A2 glutamate transporter in colon cancer (APIP/SLC1A2), RAF1 kinase in pancreatic cancer (ATG7/RAF1) and anaplastic astrocytoma (BCL6/RAF1), EWSR1 in melanoma (EWSR1/CREM), CDK6 kinase in T-cell acute lymphoblastic leukemia (FAM133B/CDK6), and CLTC in breast cancer (CLTC/VMP1). Notably, while these fusions involved known cancer genes, all occurred with novel fusion partners and in previously unreported cancer types. Moreover, several constituted druggable targets (including kinases), with therapeutic implications for their respective malignancies. Lastly, breakpoint analysis identified new cell line models for known rearrangements, including EGFRvIII and FIP1L1/PDGFRA. Taken together, we provide a robust approach for gene fusion discovery, and our results highlight a more widespread role of fusion genes in cancer pathogenesis.

Gene fusions represent an important class of cancer genes, created by rearrangements of the genome that bring together two different genes. Because they are unique to cancer cells, gene fusions are ideal diagnostic markers and therapeutic targets. While gene fusions were once thought restricted mainly to blood cancers, recent discoveries suggest they are more widespread. Here, we have developed an approach for mining DNA microarray data to detect the tell-tale signatures of gene fusions, as “breakpoints” occurring within the encoding DNA or expressed transcripts. We apply this approach to a large collection of nearly 1,000 human cancer specimens. From this analysis, we discover and verify twelve new gene fusions occurring in diverse cancer types. We verify that some of these rearrangements recur in other samples of the same cancer type (supporting a causal role) and that the cancers show dependency on the fusion for cancer cell growth. Notably, some of these fusions (e.g. CEP85L/ROS1 in angiosarcoma) represent the first for that cancer type and thus provide important new biological insight. Some are also good drug targets (including rearrangements of ROS1, RAF1, and CDK6 kinases), with clear implications for therapy.

Mouse models of sarcomas: critical tools in our understanding of the pathobiology

Sarcomas are neoplastic malignancies that typically arise in tissues of mesenchymal origin. The identification of novel molecular mechanisms leading to sarcoma formation and the establishment of new therapies has been hampered by several critical factors. First, this type of cancer is rarely observed in the clinic with fewer than 15,000 newly cases diagnosed each year in the United States. Another complicating factor is that sarcomas are extremely heterogeneous as they arise in a multitude of tissues from many different cell lineages (e.g. bone (osteosarcoma), fat (liposarcoma), and muscle (myosarcoma)). The scarcity of clinical samples coupled with its inherent heterogeneity creates a challenging experimental environment for clinicians and scientists. Faced with these challenges, there has been extremely limited advancement in treatment options available to patients as compared to other cancers. In order to glean insight into the pathobiology of sarcomas, scientists are now using in vivo mouse models whose genomes have been specifically tailored to carry gene deletions, gene amplifications, and point mutations commonly observed in human sarcomas. The use of these model organisms has been successful in increasing our knowledge and understanding of how alterations in relevant oncogenic, tumor suppressive, and signaling pathways directly impact sarcomagenesis. It is the goal of many in the biological community that the use of these mouse models will serve as powerful in vivo tools to further our understanding of sarcomagenesis and potentially identify new therapeutic strategies.

The role of imaging for translational research in bone tumors

Sarcomas are a heterogeneous group of rare connective tissue tumors, representing 1% of adult and 15% of childhood cancers for which biological and pathological information is still incomplete. In bone tumors patients with metastatic disease at onset, those who relapse and those with post-surgical secondary lesions still have a dismal outcome because of poor response to current therapies. Different molecular biology approaches have identified activated cell signalling pathways or specific molecular endpoints that may be considered potential drug targets or markers useful for diagnosis/prognosis in musculoskeletal pathology. Recently, advances in the field of molecular imaging allow visualization of cell and metabolic functions with the use of targets that include cell membrane receptors, enzymes of intracellular transport. Moreover advanced non-invasive newer imaging techniques like 18-FDG PET, quantitative dynamic-contrast MR imaging, diffusion weighted imaging have all shown a potential in distinguish malignant from benign lesions, in revealing the efficacy of therapy in tumors, the onset of recurrence and a good reliability in reckoning the percentage of necrosis in Ewing sarcoma and osteosarcoma. Thus, in vivo detection of imaging cancer biomarkers may be useful to better characterize those complex pathologic processes, such as apoptosis, proliferation and angiogenesis that determine tumor aggressiveness, providing not only complementary information of prognostic metabolic indicators, but also data in real-time on the efficacy of the treatment through the modulation of the cell metabolism.

MicroRNA cloning and sequencing in osteosarcoma cell lines: differential role of miR-93

BACKGROUND

Studies show that abnormalities in non-coding genes can contribute to carcinogenesis; microRNA levels may modulate cancer growth and metastatic diffusion.

METHOD

MicroRNA libraries were built and sequenced from two osteosarcoma cell lines (MG-63 and 143B), which differ in proliferation and transmigration. By cloning and transfection, miR-93, expressed in both cell lines, was then investigated for its involvement in osteosarcoma progression.

RESULTS

Six of the 19 miRNA identified were expressed in both cell lines with higher expression levels of miR-93 in 143B and in primary osteosarcoma cultures compared to normal osteoblasts. Interestingly, levels of miR-93 were significantly higher in metastases from osteosarcoma than in paired primary tumours. When 143B and MG-63 were transfected with miR-93, clones appeared to respond differently to microRNA overexpression. Ectopic expression of miR-93 more significantly increased cell proliferation and invasivity in 143B than in MG-63 clones. Furthermore, increased mRNA and protein levels of E2F1, one of the potential miR-93 targets, were seen in osteosarcoma cellular clones and its involvement in 143B cell proliferation was confirmed by E2F1 silencing.

CONCLUSION

Although further studies are needed to evaluate miRNA involvement in osteosarcoma progression, miR-93 overexpression seems to play an important role in osteosarcoma cell growth and invasion.

[What is new in the local approach of limb sarcomas and desmoid tumours?]

The treatment of soft tissue sarcomas of limbs should be discussed within an experienced multimodality team. Surgical resection remains the cornerstone of therapy for localized disease and achieves a five years overall survival around 75% and a local recurrence rate as low as 10% in the best series. In complex cases, neo-adjuvant treatments may be used such as systemic chemotherapy, isolated limb perfusion, or radiotherapy to achieve an optimal conservative approach. Molecular genetics of sarcomas and quality of margins are essential to guide diagnosis and therapeutic selection. In case of marginal or incomplete resection, a new enlarged surgical resection should always be discussed before administration of any adjuvant treatments. Many retrospective studies and two randomized studies (one of adjuvant brachytherapy and one of external beam radiotherapy) have shown that adjuvant radiotherapy after complete surgery significantly reduces the risk of local recurrence in extremity soft tissue sarcomas. A randomized study has compared pre- to postoperative radiotherapy. The results in terms of local control are similar in both arms. The risk of surgical complications is higher in the preoperative arm and the risk of late sequelae is higher in the postoperative arm. A randomized study within the French sarcoma group is ongoing evaluating the omission of postoperative radiotherapy in favourable cases. Presently, the role of systematic first-line invasive treatment (including surgery and/or radiotherapy) of desmoids is debated. It is becoming evident that up to 50% of patients with desmoids benefit from a front-line non-aggressive policy, because growth arrest is a common feature of this disease. Additional study of the molecular determinants of desmoid behaviour is needed to guide treatment.