MAPPYACTS (NCT02613962) is an international prospective precision medicine trial aiming to define tumor molecular profiles in pediatric patients with recurrent/refractory malignancies, in order to suggest the most adapted salvage treatment. From February 2016 to July 2020, 787 patients were included in France, Italy, Ireland and Spain. At least one genetic alteration leading to targeted treatment suggestion was identified in 436 patients (69%) with successful sequencing; 10% of these were considered "ready for routine use". Of 356 patients with follow-up beyond 12 months, 107 (30%) received one or more matched targeted therapies, 56% of them within early clinical trials, mainly in the AcSé-ESMART platform trial (NCT02813135). Overall, matched treatment resulted in a 17% objective response rate, those of patients with "ready for routine use" alterations was 38%. In patients with extra-cerebral tumors, 76% of actionable alterations detected in tumor tissue were also identified in circulating cell free DNA (cfDNA).

This single-institutional feasibility study prospectively characterized genomic alterations in recurrent or refractory solid tumors of pediatric patients to select a targeted therapy. Following treatment failure, patients with signed consent and ages above 6 months, underwent tumor biopsy or surgical resection of primary or metastatic tumor site. These newly acquired samples were analyzed by comparative genomic hybridization array, next-generation sequencing for 75 target genes, whole-exome and RNA sequencing. Biological significance of the alterations and suggestion of most relevant targeted therapies available were discussed in a multidisciplinary tumor board. From December 2012 to January 2016, 75 patients were included, 73 patients underwent 79 interventions, 56 of which were research biopsies with a low complication rate. All patients were pretreated, 37.0% had a brain tumor, and 63.0% had an extra-cranial solid tumor. Median tumor cell content was 70% (range, 0%-100%). Successful molecular analysis in 69 patients detected in 60.9% of patients an actionable alteration in various oncogenic pathways (42.4% with copy-number change, 33.3% with mutation, 2.1% with fusion), and change in diagnosis in three patients. Fourteen patients received 17 targeted therapies; two had received a matched treatment before inclusion. Research biopsies are feasible in advanced pediatric malignancies that exhibit a considerable amount of potentially actionable alterations. Genetic events affecting different cancer hallmarks and limited access to targeted agents within pediatric clinical trials remain the main obstacles that are addressed in our two subsequent precision medicine studies MAPPYACTS and AcSé-ESMART. .

Pediatric cancers differ from adult tumors, especially by their very low mutational rate. Therefore, their etiology could be explained in part by other oncogenic mechanisms such as chromosomal rearrangements, supporting the possible implication of fusion genes in the development of pediatric cancers. Fusion genes result from chromosomal rearrangements leading to the juxtaposition of two genes. Consequently, an abnormal activation of one or both genes is observed. The detection of fusion genes has generated great interest in basic cancer research and in the clinical setting, since these genes can lead to better comprehension of the biological mechanisms of tumorigenesis and they can also be used as therapeutic targets and diagnostic or prognostic biomarkers. In this review, we discuss the molecular mechanisms of fusion genes and their particularities in pediatric cancers, as well as their relevance in murine models and in the clinical setting. We also point out the difficulties encountered in the discovery of fusion genes. Finally, we discuss future perspectives and priorities for finding new innovative therapies in childhood cancer.

We hypothetized that pediatric cancers would more likely harbor fusion transcripts. To dissect the complexity of the fusions landscape in recurrent solid pediatric cancers, we conducted a study on 48 patients with different relapsing or resistant malignancies. By analyzing RNA sequencing data with a new in-house pipeline for fusions detection named Chim-Comp, followed by verification by real-time PCR, we identified and classified the most confident fusion transcripts (FTs) according to their potential biological function and druggability. The majority of FTs were predicted to affect key cancer pathways and described to be involved in oncogenesis. Contrary to previous descriptions, we found no significant correlation between the number of fusions and mutations, emphasizing the particularity to study pre-treated pediatric patients. A considerable proportion of FTs containing tumor suppressor genes was detected, reflecting their importance in pediatric cancers. FTs containing non-receptor tyrosine kinases occurred at low incidence and predominantly in brain tumors. Remarkably, more than 30% of patients presented a potentially druggable high-confidence fusion. In conclusion, we detected new oncogenic FTs in relapsing pediatric cancer patients by establishing a robust pipeline that can be applied to other malignancies, to detect and prioritize experimental validation studies leading to the development of new therapeutic options.

Recently, we detected a new fusion transcript LMO3-BORCS5 in a patient with Ewing sarcoma within a cohort of relapsed pediatric cancers. LMO3-BORCS5 was as highly expressed as the characteristic fusion oncogene EWS/FLI1. However, the expression level of LMO3-BORCS5 at diagnosis was very low. Sanger sequencing depicted two LMO3-BORCS5 variants leading to loss of the functional domain LIM2 in LMO3 gene, and disruption of BORCS5. In vitro studies showed that LMO3-BORCS5 (i) increases proliferation, (ii) decreases expression of apoptosis-related genes and treatment sensitivity, and (iii) downregulates genes involved in differentiation and upregulates proliferative and extracellular matrix-related pathways. Remarkably, in vivo LMO3-BORCS5 demonstrated its high oncogenic potential by inducing tumors in mouse fibroblastic NIH-3T3 cell line. Moreover, BORCS5 probably acts, in vivo, as a tumor-suppressor gene. In conclusion, functional studies of fusion oncogenes at relapse are of great importance to define mechanisms involved in tumor progression and resistance to conventional treatments.

In the area of precision medicine we initiated the multi-centric, international trials MAPPYACTS ‘A multicentric, prospective proof-of-concept study MoleculAr Profiling for Pediatric and Young Adult Cancer Treatment Stratification’ (NCT02613962) and AcSé-ESMART ‘European Proof-of-Concept Therapeutic Stratification Trial of Molecular Anomalies in Relapsed or Refractory Tumors’ (NCT02813135). Design: Patients with pediatric recurrent or refractory malignancy underwent on-purpose tumor biopsy or surgical resection for molecular characterization by whole exome and RNA sequencing. A molecular tumor board of scientists and clinician-scientists reviewed results to determine the biological significance of the alterations which were discussed with the treating physician in a clinical molecular tumor board. Patients were treated whenever possible in an adapted clinical trial or the hypothesis-driven ESMART proof-of concept trial for which comprehensive molecular profile at relapse was mandatory and an enrichment strategy was applied. Results: From February 2016 to January 2017, 174 patients with a median age of 13 years (range, 1-32) were included in MAPPYACTS in 11 French centers. 39% had sarcomas, 25% brain tumors, 24% other solid tumor, 12% hematological malignancies. Currently, 104 patients have been completely analyzed and discussed. Of these, screening failed for 8.6% of patients. 95 patients underwent intervention by biopsy (72%), surgical resection (24%) or blood/bone marrow sampling (4%). Sufficient material was achieved in 81% of patients, 76 had whole exome, 68 RNA, 1 panel gene sequencing. For 76% of patients, at least one target was found that was considered ‘actionable’ and a total of 123 genomic alterations were decisional for the treatment suggestion. Alterations were CNA (56/123), somatic mutation (41), CNA + somatic mutation (11), gene fusion (6), germline mutation (3) germline mutation + CNA (3), CNA + fusion (2), expression (1). Based on the detected alteration, 21 patients were included in the ESMART trial since it opened in August 2016, two of these patients were included in two different arms: with the CDK4/6 inhibitor ribociclib plus chemotherapy (1) or everolimus (5), DNA repair interfering combinations WEE1 inhibitor AZD1775 plus chemotherapy (4) and PARP inhibitor olaparib plus chemotherapy (1), dual mTOR inhibitor vistusertib alone (1) or with chemotherapy (5), or nivolumab and cyclophosphamide (6). 15 of the 23 inclusions were considered enriched as per detected alteration. 5 patients were included in other early clinical trials with a targeted agent. Updated results will be presented at the meeting. Conclusion: MAPPYACTS shows the feasibility in a multicentric setting and confirms that actionable molecular alterations are frequently found in recurrent pediatric cancers. However few tumors have unique targetable driver events and proof-of-concept trials are crucial to explore innovate combination strategies in an enriched setting. Citation Format: Birgit Geoerger, Gudrun Schleiermacher, Gaelle Pierron, Ludovic Lacroix, Marc Deloger, Nadia Bessoltane, Anne Catherine Harttrampf, Stefan Michiels, Jean Yves Scoazec, Paul Freneaux, Xavier Paoletti, Olivier Delattre, Natalie Hoog-Labouret, Gilles Vassal. European pediatric precision medicine program in recurrent tumors: first results from MAPPYACTS molecular profiling trial towards AcSe-ESMART proof-of-concept study [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr CT004. doi:10.1158/1538-7445.AM2017-CT004

ABSTRACT. Radio-iodinated metaiodobenzylguanidine ( 123 I-MIBG) is used for the detection and staging of neuroblastoma, pheochromcytoma and other neuroendocrine tumours in diagnostic nuclear medicine. A specific uptake and storage mechanism provides the basis for imaging with

Background Epithelioid sarcomas and rhabdoid tumors are rare, aggressive malignancies with poor prognosis. Both are characterized by INI1 alterations and deregulation of growth factor receptors albeit their interaction has not been elucidated. Methods In this study, we investigated the activity of a panel of epigenetic modulators and receptor tyrosine kinase inhibitors in vitro on respective cell lines as well as on primary patient-derived epithelioid sarcoma cells, and in vivo on xenografted mice. Focusing on histone deacetylase (HDAC) inhibitors, we studied the mechanism of action of this class of agents, its effect on growth factor receptor regulation, and changes in epithelial-to-mesenchymal transition by using cell- and RT-qPCR-based assays. Results Pan-HDAC inhibitor panobinostat exhibited potent anti-proliferative activity at low nanomolar concentrations in A204 rhabdoid tumor, and VAESBJ/GRU1 epithelioid sarcoma cell lines, strongly induced apoptosis, and resulted in significant tumor growth inhibition in VAESBJ xenografts. It differentially regulated EGFR, FGFR1 and FGFR2, leading to downregulation of EGFR in epithelioid sarcoma and to mesenchymal-to-epithelial transition whereas in rhabdoid tumor cells, EGFR was strongly upregulated and reinforced the mesenchymal phenotype. All three cell lines were rendered more susceptible towards combination with EGFF inhibitor erlotinib, further enhancing apoptosis. Conclusions HDAC inhibitors exhibit significant anticancer activity due to their multifaceted actions on cytotoxicity, differentiation and drug sensitization. Our data suggest that the tailored, tissue-specific combination of HDAC inhibitors with therapeutics which target cellular salvage mechanisms might increase their therapeutic relevance.