Novel Molecular Targets for Drug Development in Non-GIST Sarcomas

February 26, 2016

In this review, Rodrigo R. Muhoz, MD, William D. Tap, MD, and Sandra P. D'Angelo, MD address the emerging therapeutic strategies aimed at specific molecular targets that could potentially change the approach to patients with soft-tissue sarcomas.

Abstract

The characterization of molecular abnormalities implicated in the tumorigenesis of sarcomas is being increasingly applied to the classification, prognostication, and in particular situations, management of these diseases. Although the treatment for the majority of patients still relies on conventional cytotoxic agents, the elucidation of underlying genetic aberrations and mechanisms of these diseases are gradually translating into therapeutic progress. In this review, we address the emerging therapeutic strategies aimed at specific molecular targets that could potentially change the approach to patients with soft-tissue sarcomas.

Introduction

Sarcomas represent a diverse group of neoplasms of mesenchymal origin that correspond to approximately 1.5% of all malignancies in adults.1-4Genetic aberrations in sarcomas occur as either simple karyotypic abnormalities, such as chromosomal translocations, amplifications, and deletions, or complex/unbalanced karyotypic changes that result from accumulated nonspecific gains and losses. Chromosomal translocations associated with gene fusions and subsequent transcriptional dysregulation account for the majority of the genetic hallmarks identified in sarcomas.5,6In addition to the formation of chimeric transcription factors involving oncogenes, translocations may prompt the activation of proteins with tyrosine kinase function or autocrine growth factors. Conversely, tumors without specific cytogenetic abnormalities are characterized by genome instability, which results in multiple and alternative genomic aberrations of unclear significance and a complex karyotype.5-7

One of the major breakthroughs that emerged from a molecular-based approach is exemplified in gastrointestinal stromal tumors (GIST).8-11Despite this initial enthusiasm, targeting molecular alterations has been less fruitful in other histologies, in which genetic alterations rarely act as driver mutations. Nevertheless, the evolving molecular characterization and widespread use of next-generation sequencing techniques has unveiled a series of new potential targets through a better characterization on the molecular landscape. In this review, we will focus on novel potential molecular targets in non-GIST sarcomas, based on available clinically-relevant results.

PDGFR in Sarcomas

Platelet-derived growth factor receptors (PDGFRs) are tyrosine-kinase receptors consisting of either α- or β-chains forming 3 possible receptors: PDGFR-αα, PDGFR-αβ, and PDGFR-ββ. The activation of PDGFR occurs upon interaction with platelet-derived growth factor (PDGF) ligands in the extracellular domain, which include 5 different isoforms.

After dimerization, each PDGFR partner phosphorylates tyrosine residues located on the cytosolic tails.12Across different subtypes of sarcomas, signaling through PDGF/PDGFR has been shown to promote progression through cell cycle and avoidance of apoptosis, and result in pro-angiogenic effects and modulation of the tumor stroma.13-18Activation of PDGFR results in downstream signaling through multiple pathways involving phosphatidylinositol-3-kinase (PI3K), phospholipase-C gamma (PLCγ), Rous sarcoma oncogene (SRC) kinases and rat sarcoma oncogene (RAS)/mitogen-activated protein kinase (MAPK) proteins.13In normal cells, high expression of PDGFRβ is seen in fibroblasts, pericytes and smooth muscle, and PDGFRα in megakaryocytes, fibroblasts, myoblasts, pericytes, smooth muscle, and neurons.14Across different subtypes of sarcomas, signaling through PDGF/PDGFR has been shown to promote progression through cell cycle and avoidance of apoptosis, and result in pro-angiogenic effects and modulation of the tumor stroma.13-19

In dermatofibrosarcoma protuberans (DFSP), inhibition of PDGFβ/PDGFRβ with tyrosine kinase inhibitors20-25, showed significant clinical activity, culminating with the approval of imatinib by the US Food and Drug Administration (FDA) for the treatment of patients with advanced/ metastatic disease.20-25The molecular hallmark of DFSP is the recurrent translocation t(17;22) (q22;q13), that results in the fusion of the collagen type I alpha 1 (COL1A1) promoter to PDGF, leading to constitutive activation of this pathway.20In a pooled analysis including 24 patients treated with imatinib, objective response rate (ORR) was 46% and median time to tumor progression (mTTP) was 1.7 years.25

In addition, the PDGF/PDGFR pathway has been associated with the pathogenesis of different sarcomas including rhabdomyosarcoma, Kaposi’s sarcoma, synovial sarcoma, chondrosarcoma, osteosarcoma, and Ewing family sarcoma. Elevated expression of PDGFβ and co-expression of PDGFβ and PDGFRα has been correlated with high histological grades and poor prognosis in sarcomas.17,18Postulated mechanisms include the modulation of angiogenesis, regulation of stroma-derived fibroblasts and autocrine stimulation of cellular growth.16Overexpression of mRNA for PDGFRα and PDGF has been documented in sarcoma, highlighting the relevance of this autocrine loop.16In addition, preclinical data suggest that blocking PDGF/PDGFR results in a potentiation of response to chemotherapy.15

Pazopanib, an oral, multi-targeted tyrosine kinase inhibitor also active against PDGFR, was shown to prolong progression-free survival (PFS) versus placebo in pretreated patients with advanced non-adipocytic soft tissue sarcomas (median PFS, 4.6 months vs 1.6 months; hazard ratio [HR], 0.31; P <.0001) in a phase III trial, and is currently approved by the FDA for clinical use.26Similarly, regorafenib, a distinct multikinase inhibitor, resulted in improved PFS in previously treated patients with leio- myosarcoma (4.0m vs 1.9m; HR 0.49; p=0.017) and other soft-tissue sarcomas (4.6m vs 1.0m; HR 0.38; p=0.002) in a randomized, placebo controlled, phase II study. In line with these observations, two partial responses were seen in a series of 31 patients with PDGFRb-expressing solitary fibrous tumors (SFT) treated with sunitinib, also a tyrosine-kinase inhibitor. Of note, recent studies revealed a 12q13 intrachromossomal fusion in SFT, resulting in the NAB2:STAT6 fusion protein and subsequent transcriptional activation of several genes and expression of receptor tyrosine kinases.

More recently, approaches focusing on more specific inhibition of PDGFRα with olaratumab led to promising results. Olaratumab (IMC-3G3) is a recombinant IgG1-type monoclonal antibody that binds with high affinity to PDGFRα and prevents PDGF from binding to the receptor; olaratumab also blocks downstream signaling through Akt and mitogen-activated protein kinase (MAPK).16The results of a phase 1b/2 study evaluating the efficacy of doxorubicin with or without olaratumab have been recently presented. In the randomized phase II portion of the study including 133 patients, the addition of olaratumab resulted in a dramatic gain in overall survival (OS) (median OS 25m vs 14.7m; HR 0.441; p=0.0004), despite only a marginal improvement in PFS (median PFS 6.6m vs 4.1m; HR 0.672; p=0.0615). Noteworthy, adverse events leading to treatment discontinuation were less frequent in the combination arm (13% versus 22%). A pivotal phase III trial addressing this combination in comparison to doxorubicin and placebo is currently ongoing (NCT02451943).

Potential Targets for Inhibition: KDR, PTPRB, and PLCG1 in Angiosarcomas

Angiosarcomas (ASs) are malignancies of vascular origin associated with a significant risk of metastases and poor prognosis.27,28In addition to its vascular origin, plentiful evidence indicates the activation of pro-angiogenic pathways in the development of ASs, including overexpression of vascular endothelial growth factor (VEGF) and vascular endothelial growth factor receptors (VEG- FRs).29,30Bevacizumab, a recombinant monoclonal antibody targeting VEGF-A, was studied in a single arm, phase II trial in patients with tumors of vascular origin (AS, N=23; epithelioid hemangioendothelioma, N=7). Four objective responses occurred (2 patients with AS and 2 patients with epithelioid hemangioendothelioma), resulting in an ORR of 17%; 15 patients (50%) (N=15) achieved stable disease and median PFS was 12.4 weeks.31In the recently presented ANGIOTAX-PLUS study, patients with AS were randomized to receive weekly paclitaxel with or without bevacizumab.

There were no statistically significant differences in ORR (40% vs 50%), median PFS (6.8 months vs 6.9 months), or median OS (19.5 months vs 15.9 months) between treatment arms.32 Sorafenib, a multi-targeted tyrosine kinase inhibitor with anti-angiogenic properties, was investigated in a prospective study encompassing different histologies.33Among a subset of 37 evaluable AS patients, ORR was 14% and median PFS was 3.8 months, with the majority of patients with AS having stable disease as best response.33Similarly, sorafenib resulted in response rates of 0% and 14.6% and transient tumor control in phase II trials reported by von Mehren et al35 and Ray-Coquard et al34, respectively. Recent studies applying whole genome, whole exome, and targeted sequencing techniques provided further insight into potential therapeutic targets in ASs.

Using gene expression profiling, Antonescu et al showed upregulation of vascular-specific receptor tyrosine kinases, including kinase insert domain receptor (KDR) and tyrosine kinase with immunoglobulin-like and EGF-like domains 1 (TIE1) and FLT1. Of note, KDR gene mutations were associated with high expression of KDR protein and occurred in 10% of patients with ASs (all arising from the breast).29In an analysis of 26 primary and 29 secondary ASs, Styring et al36 demonstrated significant deregulation of 103 genes. Once again, secondary ASs showed a genetic signature distinct from primary ASs, with upregulation of MYC, KIT, and RET and downregulation of CDKN2C.36 Behjati et al37 reported at least 1 driver mutation in angiogenesis signaling genes in 15 of 39 ASs (38%), the most common being MYC. Of note, these driver mutations were not mutually exclusive.37 PTPRB truncating mutations were found in 26% (10 out of 39) of AS samples and exposure of PTPRB-silenced cell cultures to sunitinib or vatalanib resulted in suppression of angiogenesis. In addition, activating mutations of PLCG1, a signal transducer of tyrosine kinases involved in cell growth, signaling, and maintenance of membrane phospholipids, were documented in 9% of the cases.37

In line with these observations, a retrospective series investigating the effects of sorafenib in cohorts limited to patients with RT-associated AS of the breast found MYC and FLT4 coamplification in 2 out of 3 patients with objective responses (in total, 9 patients were assessable for response; ORR = 33%).38In summary, although objective responses are limited to a subset of patients, tyrosine kinase inhibitors and agents targeting angiogenesis are active and able to induce disease stabilization in unselected AS patients, representing a reasonable alternative beyond conventional cytotoxic chemotherapy. Findings from molecularly based studies provide conceptual models for fur- ther investigation of anti-angiogenic therapies in AS.

ALK in Inflammatory Myofibroblastic Tumors

Inflammatory myofibroblastic tumors (IMTs) are tumors composed of spindle cell proliferation mixed with a collagenous stroma in an inflammatory background of granulocytes, lymphocytes, and plasma cells.39In almost 50% of the cases, IMT harbors chromosomal aberrations that result in rearrangements involving the anaplastic lymphoma kinase (ALK) locus on chromosome 2p23 or increased copy numbers without rearrangement. The product of this genetic variation is a receptor tyrosine kinase (RTK) that is constitu-tively activated, leading to cell growth and tumorigenesis.40Crizotinib is an oral tyrosine kinase inhibitor targeting ALK, MET, and ROS1 that was initially approved for the treatment of patients with non—small-cell lung cancer. Recently, Butrynski et al reported a partial response in a patient with ALK-rearranged IMT treated with crizotinib, suggesting that this agent might also be effective in treating patients with ALK-rearranged IMT.41 Given these promising results and based on a strong rationale, a phase II trial is ongoing (NCT01524926).

MDM2 and CDK4 in Well-Differentiated/ Dedifferentiated Liposarcoma

Liposarcomas are soft tissue sarcomas of adipocytic origin that comprise different histologic subtypes, including well-differentiated liposarcoma (WDLPS) and dedifferenti- ated liposarcoma (DDLPS).4

WDLPS and DDLPS are marked by amplifications in- volving chromosome 12, which occur in more than 80% to 90% of the cases.42-44These 12q gains result in co-amplification of cyclin-dependent kinase 4 (CDK4) and MDM2 oncogenes. Several agents targeting MDM2 and CDK4 are currently in development, although the success rate with inhibitors used as single agents has been limited.

CDK4 is a cyclin-dependent kinase that regulates the G1—S phase transition in the cell cycle and promotes tumorigenesis through inhibition of the retinoblastoma (Rb) protein family.45Following prolonged disease stabilization in patients with WDLPS/DDLPS in a phase I trial,46our group reported the results of a phase II trial with the CDK4/6 inhibitor palbociclib (PD0332991), which demonstrated a PFS rate of 66% at 12 weeks. Among 29 evaluable patients with CDK4 amplification enrolled in the therapeutic cohort, the median PFS was 18 weeks.47Palbociclib was recently approved by the FDA for the treatment of patients with breast cancer. LEE011, a distinct orally bioavailable CDK4/6 inhibitor, was also shown to be tolerable and able to induce long-lasting disease stabilizations in a phase I clinical trial including multiple solid tumors. Stable disease sustained for more than 4 and 6 cycles occurred in 26% and 14% of the patients, respectively.48Additional studies to better characterize the efficacy of LEE011 are ongoing (NCT01237236, NCT02187783, NCT02343172).

The MDM2 gene encodes an E3 ubiquitin ligase that binds to tumor suppressor p53 and targets p53 for proteasomal degradation. Therefore, MDM2 amplification/over-expression lead to increased p53 inactivation and result in a pro-oncogenic effect. In a pilot study investigating the oral MDM2 inhibitor RO5045337 (also known as RG7112), both reactivation of the p53 pathway and decreased cell proliferation were demonstrated between pre- and post-treatment biopsies.49 Among 20 patients, there was 1 partial response and 14 patients achieved disease stabilization.

In another phase I dose escalation study that included a sarcoma extension cohort, RO5045337/RG7112 demonstrated manageable toxicities, biomarker activity, and objective responses in patients with liposarcomas.50 Nevertheless, the same drug in combination with doxorubicin (NCT01605526) resulted in high incidence of neutropenia and thrombocytopenia.51

Additional agents targeting MDM2 are currently un- der clinical development. These include SAR405838, presently being investigated in early-phase clinical tri- als (NCT01636479, NCT01985191), and AMG-232, a MDM2 inhibitor derived from AM-8553 (NCT01723020, NCT02110355).

Microphthalmia Family Transcription Factors in Alveolar Soft Part Sarcomas and Clear Cell Sarcomas

The microphthalmia (MiT) family transcription factors include MITF, TFE3, TFEB, and TFEC, which are involved in regulation of cell growth, differentiation, and survival. Dysregulation of MiT family members results in aberrant activation of multiple genes, including c-Met. This leads to oncogenesis in different cancer types and is thought to be particularly relevant in alveolar soft part sarcoma (ASPS) and clear cell sarcoma (CCS).52The c-Met product is a receptor tyrosine kinase activated upon interation with hepatocyte growth fact (HGF) frequently expressed in mesenchymal cells and also linked to intracellular signaling through intracellular signaling MAPK and AKT path- ways,53providing a rationale for further study of MET and other TKI inhibitors in ASPS and CCS.

In ASPS, TFE is fused to the ASPL gene as a consequence of a typical unbalanced t(X;17)(p11;q25) translocation, resulting in the ASPL-TFE3 fusion protein. Although the function of ASPL needs to be further clarified, TFE3 acts as a transcription factor and the fusion transcripts lead to MET transcriptional upregulation through the cMet gene.54

Also an MiT-associated tumor, CCS expresses different cytogenetic abnormalities. Typically, EWSR1-ATF1 fusion results from the t(12;22)(q13;q12) translocation55,56; in a smaller subset of patients, t(2;22)(q34;q12) translocation produces a EWSR1-CREB1 fusion-gene.57These abnormalities induce MITF and c-Met expression. In preclinical models, blockade of c-Met activity and HGF resulted in CCS cell growth arrest.53Disappointingly, a phase II study of the MET inhibitor tivatinib in MITF-associated tumors produced no objective responses in 27 ASPS patients. In the same trial, only 1 objective response occurred among 11 patients with CCS.58

In both entities (ASPS and CCS), although responses were seen with multi-targeted tyrosine kinase inhibitors, the role of MET inhibitors remains to be further investigated and a clinical trial with cabozantinib is ongoing (NCT01755195).

The PI3K-Akt-mTOR Pathway in PEComas, Myxoid/ Round Cell Liposarcomas, and Angiosarcomass The phosphotidylinositol 3-kinase (PI3K)-Akt-mammalian target of rapamycin (mTOR) is a key pathway in the control of cell proliferation, survival, and angiogenesis. Several pre-clinical and translational studies have addressed the role of the PI3KAkt- mTOR pathway and investigated the mecha- nism of action of mTOR inhibitors; evidences of activation of this pathway have been well demonstrated in sarcomas.59-63

Ridaforolimus showed some degree of activity in phase I/II studies,64,65but failed to demonstrate a survival benefit when used as a maintenance therapy in a randomized phase III trial (P= .46).66 Different mTOR inhibitors, in- cluding temsirolimus, everolimus, and sirolimus, were also evaluated in small prospective trials.67-70

Despite limited efficacy in unselected patients with sarcomas, a histology-driven approach could further clarify the role of mTOR inhibitors in the treatment of this group of malignancies. Perivascular epithelioid cell tumors (PEComas) are rare mesenchymal neoplasms that exhibit features of both smooth muscle and melanocytic origin4,71and are often characterized by the presence of inactivating mutations in tuberous sclerosis complex (TSC) genes TSC1 and TSC2, which are upstream inhibitors of the mTOR complex 1 (mTORC1).72Although data are limited due to the rarity of this disease, durable responses have been reported with sirolimus and everolimus. In a series of 5 patients with non-pulmonary PEComas treated with sirolimus or everolimus, 3 complete responses and 1 partial response occurred. Molecular studies identified TSC2 aberrations in 4 of these patients.73

Barretina et al reported a relatively high prevalence of PIK3CA mutations (18%) in patients with myxoid/round-cell liposarcomas.45Similarly, Demicco et al showed that although activating PIK3CA mutations occurred in only 14% of the cases and more frequently in round cell than myx- oid tumors (33% vs 3%; P = .013), additional mechanism for PI3K/Akt activation were observed, including loss of PTEN and upregulation of IGF1R.74

In angiosarcomas, activation of the PI3K/Akt/mTOR pathway occurs as a result of VEGF downstream signaling, involving mTORC1, mTORC2, and phosphorylation of p70 S6-kinase (S6K). In preclinical models, the growth of AS cell lines was supressed by celecoxib and rapamycin,75 and inhibition of mTORC1, mTORC2, and phosphorylation of Akt was demonstrated.76

In addition to conventional mTOR inhibitors, there has been growing interest in the investigation of dual PI3K- mTOR inhibitors in these diseases, including BEZ235 (NCT01690871), VS5584 (NCT01991938), and DS7423 (NCT01364844).

IDH1 Mutations in Chondrosarcomas

The isocitrate dehydrogenase protein (IDH) family comprises 3 enzymes, IDH1, IDH2, and IDH3, which show different intracellular spatial distributions. These isoenzymes are involved in the oxidative decarboxylation of isocitrate. Mutations in genes encoding IDH1 and IDH2 result in proteins with aberrant enzymatic activity that produce (D)-2-hydroxyglutarate (2HG). Cells with mutant IDH1 and IDH2 show accumulation of 2HG and subsequent epigenetic modifications involved in tumorigenesis.77Initially identified in gliomas, IDH mutations are present in up to 50% to 60% of chondrosarcomas.78Preclinical data suggest that differentiation of mesenchymal progenitor cells can be disrupted by transfection with IDH2 mutant constructs in mice, and that exposure to the demethylating agent 5-azacytidine was able to restore a differentiatedphenotype.79Both IDH1 (AG120) and IDH2 (AG221) inhibitors are currently under development for patients with different malignancies associated with IDH mutations, including gliomas and chondrosarcomas.

Notch Inhibition in Desmoid Tumors

Desmoid tumors (DT) (or aggressive fibromatosis) are uncommon mesenchymal neoplasms characterized by locoregional aggressiveness, despite the absence of capacity of metastatic dissemination. The molecular hallmark of DT is the deregulation of the Wnt signaling pathway, frequently associated with gain-of-function mutations involving genes enconding for b-catenin (CTNNB1). Recent studies have suggested that DT also frequently express Notch pathway components and the existence of crosstalk between Wnt and Notch pathways, with preclinical evidence providing the rationale for the clinical exploration of Notch signaling suppression through gamma-secretase inhibition.

In a phase I trial, the oral gamma-secretase inhibitor PF-03084014 resulted in 5 partial responses among 7 patients with DT (objective response rate of 71.4% in this population), with evidence of down-modulation of NOTCH-related gene expression, and further work is needed to confirm these preliminary findings.

Conclusion

While conventional cytotoxic chemotherapy remains the predominant treatment modality for patients with advanced sarcomas, genomics may continue to pave the way for the development of personalized care. Despite evidence supporting a mech- anistic rationale in different types of sarcomas, targeting these molecular aberrations translated into meaningful therapeutic and clinical benefits only in a small subset of scenarios and the use of wide molecular analyses remains investigational and limited to select clinical trials. Nevertheless, some of these discoveries begin to shape the treatment decisions in specific histologies, as exemplified by the use of mTOR inhibitors in PEComa, imatinib in DFSP, pazopanib in pre-treated, non-adipocytic sarcomas, agents targeting angiogenesis in vascular sarcomas and, potentially MDM2 and CDK4 inhibitors in lipo- sarcomas.

References

  1. Further exploration of novel targets in sarcomas demands the development of adequate cell lines and preclinical models, as well as practical tools for the selection of patients for early phase clinical trials, in order to potentiate the benefit of tailored approaches.
  2. Ducimetiere F, Lurkin A, Ranchere-Vince D, et al. Incidence of sarcoma histotypes and molecular subtypes in a prospective epidemiological study with central pathology review and molecular testing. PLoS One. 2011;6(8):e20294.
  3. Wibmer C, Leithner A, Zielonke N, et al. Increasing incidence rates of soft tissue sarcomas? a population-based epidemiologic study and literature review. Ann Oncol. 2010;21(5):1106-1111.
  4. Siegel RL, Miller KD, Jemal A. Cancer statistics, 2015. CA Cancer J Clin. 2015;65:5 -29.
  5. Fletcher C DM, Bridge JA, Hogendoorn P, et al. WHO classification of tumours of soft tissue and bone. Fourth Edition. WHO 2013;IARC WHO Classification of Tumours, No 5. ISBN-13 9789283224341
  6. Taylor BS, Barretina J, Maki RG, et al. Advances in sarcoma genomics and new therapeutic targets. Nat Rev Cancer. 2011;11(8):541-557.
  7. Frith AE, Hirbe AC, Van Tine BA. Novel pathways and molecular targets for the treatment of sarcoma. Curr Oncol Rep. 2013; 15:378-385.
  8. Jain S, Xu R, Prieto VG, et al. Molecular classification of soft tissue sarcomas and its clinical applications. Int J Clin Exp Pathol. 2010;3(4):416- 428.
  9. Miettinen M, Lasota J . Gastrointestinal stromal tumors-definition, clinical, histological, immunohistochemical, and molecular genetic features and differential diagnosis. Virchows Arch. 2001;438:1.
  10. Hirota S, Isozaki K, Moriyama Y, et al. Gain-of-function mutations of c-kit in human gastrointestinal stromal tumors. Science. 1998;279:577—580.
  11. Heinrich MC, Corless CL, Duensing A, et al. PDGFRA activating mutations in gastrointestinal stromal tumors. Science. 2003;299:708—710.
  12. Tap WE, Schwartz GK. That&rsquo;s the &ldquo;GIST&rdquo; of it: use of adjuvant imatinib after resection of a primary GI stromal tumor. J Clin Oncol. 2014;32:1543—1546.
  13. Fredriksson L, Li H, Eriksson U. The PDGF family: four gene products form five dimeric isoforms. Cytokine Growth Factor Rev. 2004;15: 197—204.
  14. Tallquist M, Kazlauskas A. PDGF signaling in cells and mice. Cytokine Growth Factor Rev. 2004;15:205—213.
  15. Östman A. PDGF receptors-mediators of autocrine tumor growth and regulators of tumor vasculature and stroma. Cytokine Growth Factor Rev. 2004;15:275—286.
  16. Pietras K, Rubin K, Sjöblom T, et al. Inhibition of PDGF receptor signaling in tumor stroma enhances antitumor effect of chemotherapy. Cancer Res. 2002;62:5476—5484.
  17. Shah GD, Loizos N, Youssoufian H. et al. Rationale for the development of IMC-3G3, a fully human immunoglobulin G subclass 1 monoclonal antibody targeting the platelet-derived growth factor receptor alpha. Cancer. 2010;116(4 suppl):1018-1026.
  18. Wang J, Coltrera MD, Gown AM et al. Cell proliferation in human soft tissue tumors correlates with platelet- derived growth factor B chain expression: an immunohistochemical and in situ hybridization study. Cancer Res.1994;54:560—564.
  19. Kilvaer TK, Valkov A, Sorbye SW, et al. Platelet-derived growth factors in non-GIST soft-tissue sarcomas identify a subgroup of patients with wide resection margins and poor disease-specific survival. Sarcoma. 2010:751304.
  20. Heldin CH, Westermark B. Mechanism of action and in vivo role of platelet- derived growth factor. Physiol Rev. 1999;79:1283-1316.
  21. Simon MP, Pedeutour F, Sirvent N et al. Deregulation of the platelet- derived growth factor B-chain gene via fusion with collagen gene COL1A1 in dermatofibrosarcoma protuberans and giant-cell fibroblastoma. Nat Genet. 1997; 15 95 - 98.
  22. McArthur GA, Demetri GD, van Oosterom A, et al. Molecular and clinical analysis of locally advanced dermatofıbrosarcoma protuberans treated with imatinib: imatinib target exploration consortium study B2225. J Clin Oncol. 2005;23:866-873.
  23. Kamar FG, Kairouz VF, Sabri AN. Dermatofibrosarcoma protuberans (DFSP) successfully treated with sorafenib: case report. Clin Sarcoma Res. 2013;3:5.
  24. Ong HS, Ji T, Wang LZ, Yu ZW et al. Dermatofibrosarcoma protuberans on the right neck with superior vena cava syndrome: case report and literature review. Int J Oral
  25. Maxillofac Surg. 2013;42:707.
  26. Maki RG, Awan RA, Dixon RH, et al. Differential sensitivity to imatinib of 2 patients with metastatic sarcoma arising from dermatofibrosarcoma protuberans. Int J Cancer. 2002;100:623-626.
  27. Rutkowski P, Van Glabbeke M, Rankin CJ, et al. Imatinib mesylate in advanced dermatofibrosarcoma protuberans: pooled analysis of two phase II clinical trials. J Clin Oncol. 2010;28:1772.
  28. van der Graaf WT, Blay JY, Chawla SP, et al. Pazopanib for metastatic soft- tissue sarcoma (PALETTE): a randomised, double-blind, placebo-controlled phase 3 trial. Lancet. 2012;19;379:1879-1886.
  29. Penel N, Italiano A, Ray-Coquard I, et al. Metastatic angiosarcomas: doxorubicin-based regimens, weekly paclitaxel and metastasectomy significantly improve the outcome. Ann Oncol. 2012; 23:517-523.
  30. Guo T, Zhang L, Chang NE, et al. Consistent MYC and FLT4 gene amplification in radiation-induced angiosarcoma but not in other radiation- associated atypical vascular lesions. Genes Chromosomes Cancer. 2011; 50:25-33.
  31. Antonescu CR, Yoshida A, Guo T, et al. KDR activating mutations in human angiosarcomas are sensitive to specific kinase inhibitors. Cancer Res. 2009;69:7175 -7179.
  32. Itakura E, Yamamoto H, Oda Y, et al. Detection and characterization of vascular endothelia growth factors and their receptors in a series of angiosarcoma. J Surg Oncol. 2008;97:74—81.
  33. Agulnik M, Yarber JL, Okuno SH, et al. An open-label, multicenter, phase II study of bevacizumab for the treatment of angiosarcoma and epithelioid hemangioendotheliomas. Ann Oncol. 2013;24:257-263.
  34. Penel N, Blay JY, Mir O, et al. ANGIOTAX-PLUS trial: A randomized phase II trial assessing the activity of weekly paclitaxel (WP) plus or minus bevacizumab (B) in advanced angiosarcoma (AS). J Clin Oncol. 2014; 32:5s (suppl; abstr 10501).
  35. Maki RG, D&rsquo;Adamo DR, Keohan ML, et al. Phase II study of sorafenib in patients with metastatic or recurrent sarcomas. J Clin Oncol. 2009;27: 3133-3140.
  36. Ray-Coquard I, Italiano A, Bompas E, et al. Sorafenib for patients with advanced angiosarcoma: a phase II trial from the French Sarcoma Group (GSF/GETO). Oncologist. 2012;7:260.
  37. von Mehren M, Rankin C, Goldblum JR, et al. Phase 2 Southwest Oncology Group-directed intergroup trial (S0505) of sorafenib in advanced soft tissue sarcomas. Cancer. 2012;118:770-776.
  38. Styring E, Seinen J, Dominguez-Valentin M et al. Key roles for MYC, KIT, and RET signaling in secondary angiosarcomas. Brit J Cancer. 2014;111: 407—412.
  39. Behjati S, Tarpey PS, Sheldon H, et al. Recurrent PTPRB and PLCG1 mutations in angiosarcoma. Nat Genet. 2014;46:376-379.
  40. D&rsquo;Angelo SP, Antonescu CR, Keohan ML, et al. Activity of sorafenib in radiation-associated breast angiosarcomas harboring MYC and FLT4 amplifications. J Clin Oncol. 2012;30 (suppl; abstr 10019).
  41. Gleason BC, Hornick JL. Inflammatory myofibroblastic tumours: where are we now? J Clin Pathol. 2008;61:428—437.
  42. Coffin CM, Patel A, Perkins S, et al. ALK1 and p80 expression and chromosomal rearrangements involving 2p23 in inflammatory myofibroblastic tumor. Mod Pathol. 2001;14:569-576.
  43. Butrynski JE, D&rsquo;Adamo DR, Hornick JL, et al. Crizotinib in ALK-rearranged inflammatory myofibroblastic tumor. N Engl J Med. 2010;363:1727—1733.
  44. Pedeutour, F, Forus A, Coindre JM, et al. Structure of the supernumerary ring and giant rod chromosomes in adipose tissue tumors. Genes Chromosomes Cancer. 1999;24:30—41.
  45. Sirvent, N, Coindre JM, Maire G, et al. Detection of MDM2CDK4 amplification by fluorescence in situ hybridization in 200 paraffin- embedded tumor samples: utility in diagnosing adipocytic lesions and comparison with immunohistochemistry and real-time PCR. Am J Surg Pathol. 2007; 31:1476—1489.
  46. Binh MB, Sastre-Garau X, Guillou L, et al. MDM2 and CDK4 immunostainings are useful adjuncts in diagnosing well-differentiated and dedifferentiated liposarcoma subtypes: a comparative analysis of 559 soft tissue neoplasms with genetic data. Am J Surg Pathol 2005;29:1340-1347.
  47. Barretina J, Taylor BS, Banerji S, et al. Subtype-specifıc genomic alterations defıne new targets for soft-tissue sarcoma therapy. Nat Genet. 2010;42:715 -721.
  48. Schwartz GK, LoRusso PM, Dickson MA, et al. Phase I study of PD0332991, a cyclin-dependent kinase inhibitor, administered in 3-week cycles (Schedule 2/1). Br J Cancer. 2011;104:1862-1868.
  49. Dickson MA, Tap WD, Keohan ML, et al. Phase II trial of the CDK4 inhibitor PD0332991 in patients with advanced CDK4-amplified well-differentiated or dedifferentiated liposarcoma. J Clin Oncol. 2013; 31:2024—2028.
  50. Infante JR, Shapiro G, Witteveen P, et al. A phase I study of the single- agent CDK4/6 inhibitor LEE011 in patients with advanced solid tumors and lymphomas. J Clin Oncol
  51. . 2014;32:5s (suppl; abstr 2528).
  52. Ray-Coquard I, Blay JY, Italiano A, et al. Effect of the MDM2 antagonist RG7112 on the P53 pathway in patients with MDM2-amplified, well- differentiated or dedifferentiated liposarcoma: an exploratory proof-of- mechanism study. Lancet Oncol. 2012;13:1133-1134.
  53. Kurzrock R, Blay JY, Nguyen BB, et al. A phase I study of MDM2 antagonist RG7112 in patients (pts) with relapsed/refractory solid tumors. J Clin Oncol 2012; 30(suppl; abstr13600).
  54. Chawla SP, Blay JY, Italiano A, et al. Phase Ib study of RG7112 with doxorubicin (D) in advanced soft tissue sarcoma (ASTS). J Clin Oncol. 2013; 31(suppl; abstr 10514).
  55. Haq R, Fisher DE. Biology and clinical relevance of the micropthalmia family of transcription factors in human cancer. J Clin Oncol. 2011;29(25):3474 -3482.
  56. Davis JI, McFadden AW, Zhang Y, et al. Identification of the receptor tyrosine kinase c-Met and its ligand, hepatocyte growth factor, as therapeutic targets in clear cell sarcoma. Cancer Res. 2010;70:639—645.
  57. Tsuda M, Davis IJ, Argani P, et al. TFE3 fusions activate MET signaling by transcriptional up-regulation, defining another class of tumors as candidates for therapeutic MET inhibition. Cancer Res. 2007;67:919—929.
  58. Wang WL, Mayordomo E, Zhang W, et al. Detection and characterization ofEWSR1/ATF1 and EWSR1/CREB1 chimeric transcripts in clear cell sarcoma (melanoma of soft parts). Mod Pathol. 2009;22:1201—1209.
  59. Jakubauskas A, Valceckiene V, Andrekute K, et al. Discovery of two novelEWSR1/ATF1 transcripts in four chimerical transcripts- expressing clear cell sarcoma and their quantitative evaluation. Exp Mol Pathol. 2011;90:194—200.
  60. Antonescu CR, Nafa K, Segal NH, et al. EWS-CREB1: a recurrent variant fusion in clear cell sarcoma—association with gastrointestinal location and absence of melanocytic differentiation. Clin Cancer Res. 2006;12:5356&ndash; 5362.
  61. Wagner AJ, Goldberg JM, Dubois SG, et al. Tivantinib (ARQ 197), a selective inhibitor of MET, in patients with microphthalmia transcription factor associated tumors: results of a multicenter phase 2 trial. Cancer. 2012;118:5894—5902.
  62. Baird K, Davis S, Antonescu CR, et al. Gene expression profıling of human sarcomas: Insights into sarcoma biology. Cancer Res. 2005;65: 9226- 9235.
  63. Hernando E, Charytonowicz E, Dudas ME, et al. The AKT-mTOR pathway plays a critical role in the development of leiomyosarcomas. Nat Med. 2007;13:748-753.
  64. Faivre S, Kroemer G, Raymond E. Current development of mTOR inhibitors as anticancer agents. Nat Rev Drug Discov. 2006;5(8):671—688.
  65. Gutierrez A, Snyder EL, Marino-Enriquez A, et al. Aberrant AKT activation drives well-differentiated liposarcoma. Proc Natl Acad Sci USA. 2011;108:16386—16391.
  66. Friedrichs N, Trautmann M, Endl E, et al. Phosphatidylinositol-30- kinase/ AKT signaling is essential in synovial sarcoma. Int J Cancer. 2011;129:1564— 1575.
  67. Mita MM, Mita AC, Chu QS, et al. Phase I trial of the novel mammalian target of rapamycin inhibitor deforolimus (AP23573; MK-8669) administered intravenously daily for 5 days every 2 weeks to patients with advanced malignancies. J Clin Oncol. 2008;26:361—367.
  68. Chawla SP, Staddon AP, Baker LH, et al. Phase II study of the mammalian target of rapamycin inhibitor ridaforolimus in patients with advanced bone and soft tissue sarcomas. J Clin Oncol. 2012;30:78—84.
  69. Demetri GD, Chawla SP, Ray-Coquard I, et al. Results of an international randomized phase III trial of the mammalian target of rapamycin inhibitor ridaforolimus versus placebo to control metastatic sarcomas in patients after benefit from prior chemotherapy. J Clin Oncol. 2013;31:2485—2492. Okuno S, Bailey H, Mahoney MR, et al. A phase 2 study of temsirolimus (CCI-779) in patients with soft tissue sarcomas: a study of the Mayo phase 2 consortium (P2C). Cancer. 2011;117:3468&ndash;3475.
  70. Schuetze SM, Zhao L, Chugh R, et al. Results of a phase II study of sirolimus and cyclophosphamide in patients with advanced sarcoma. Eur J Cancer. 2012;48:1347—1353.
  71. Yoo C, Lee J, Rha SY, et al. Multicenter phase II study of everolimus in patients with metastatic or recurrent bone and soft-tissue sarcomas after failure of anthracycline and ifosfamide. Invest New Drugs. 2013; 31:1602— 1608.
  72. Richter S, Pink D, Hohenberger P, et al. Multicenter, triple-arm, singlestage, phase II trial to determine the efficacy and safety of everolimus (RAD001) in patients with refractory bone or soft tissue sarcomas including GIST. J Clin Oncol (Meeting Abstracts). 2010;28:10038. Hornick JL, Fletcher CD. PEComas: what do we know so far? Histopathology. 2006;48:75—82.
  73. Wagner AJ, Malinowska-Kolodziej I, Morgan JA, et al. Clinical activity of mTOR inhibition with sirolimus in malignant perivascular epithelioid cell tumors: targeting the pathogenic activation of mTORC1 in tumors. J Clin Oncol. 2010;28:835—840.
  74. Dickson MA, Schwartz GK, Antonescu CR, et al. Extrarenal perivascular epithelioid cell tumors (PEComas) respond to mTOR inhibition: Clinical and molecular correlates. Int J Cancer. 2013 Apr 1; 132(7): 1711—1717.
  75. Demicco EG, Torres KE, Ghadimi MP, et al. Involvement of the PI3K/Akt pathway in myxoid/round cell liposarcoma. Mod Pathol. 2012;25: 212-221. Bundscherer A, Vogt T, Köhl G, et al. Antiproliferative effects of rapamycin and celecoxib in angiosarcoma cell lines. Anticancer Res. 2010 Oct;30:4017—4023.
  76. Du W, Gerald D, Peruzzi CA, et al. Vascular tumors have increased p70 S6-kinase activation and are inhibited by topical rapamycin. Lab Invest. 2013;93:1115—1127.
  77. Figueroa ME, Abdel-Wahab O, Lu C, et al. Leukemic IDH1 and IDH2 mutations result in a hypermethylation phenotype, disrupt TET2 function, and impair hematopoietic differentiation. Cancer Cell. 2010;18:553— 567. Amary MF, Bacsi K, Maggiani F, et al. IDH1 and IDH2 mutations are frequent events in central chondrosarcoma and central and periosteal chondromas but not in other mesenchymal tumours. J Pathol. 2011;224: 334&ndash;343.
  78. Lu C, Venneti S, Akalin A, et al. Induction of sarcomas by mutant IDH2. Genes Dev. 2013;27:1986—1998.