Novel MED15::ATF1 fusion in a pediatric melanoma with spitzoid features and aggressive presentation

Childhood melanoma is a rare and biologically heterogeneous pediatric malignancy. The differential diagnosis of pediatric melanoma is usually broad, including a wide variety of spindle cell or epithelioid neoplasms. Different molecular alterations affecting the MAPK and PI3K/AKT/mTOR pathways, tumor suppressor genes, and telomerase reactivation have been implicated in melanoma tumorigenesis and progression. Here, we report a novel MED15::ATF1 fusion in a pediatric melanoma with spitzoid features and an aggressive clinical course.

Impact of ACCELERATE Paediatric Strategy Forums: a review of the value of multi-stakeholder meetings in oncology drug development

In a landscape of an increasing number of products and histology and age agnostic trials for rare patient cancer, prioritization of products is required. Paediatric Strategy Forums, organized by ACCELERATE and the European Medicines Agency with participation of the US Food and Drug Administration, are multi-stakeholder meetings that share information to best inform pediatric drug development strategies and subsequent clinical trial decisions. Academia, industry, regulators, and patient advocates are equal members, with patient advocates highlighting unmet needs of children and adolescents with cancer. The 11 Paediatric Strategy Forums since 2017 have made specific and general conclusions to accelerate drug development. Conclusions on product prioritization meetings, as well as global master protocols, have been outputs of these meetings. Forums have provided information for regulatory discussions and decisions by industry to facilitate development of high-priority products; for example, 62% of high-priority assets (agreed at a Forum) in contrast to 5% of those assets not considered high priority have been the subject of a Paediatric Investigational Plan or Written Request. Where there are multiple products of the same class, Forums have recommended a focused and sequential approach. Class prioritization resulted in an increase in waivers for non-prioritized B-cell products (44% to 75%) and a decrease in monotherapy trials, proposed in Paediatric Investigation Plans (PIP) submissions of checkpoint inhibitors from 53% to 19%. Strategy Forums could play a role in defining unmet medical needs. Multi-stakeholder forums, such as the Paediatric Strategy Forum, serve as a model to improve collaboration in the oncology drug development paradigm.

Paediatric Strategy Forum for medicinal product development of DNA damage response pathway inhibitors in children and adolescents with cancer: ACCELERATE in collaboration with the European Medicines Agency with participation of the Food and Drug Administration

DNA damage response inhibitors have a potentially important therapeutic role in paediatric cancers; however, their optimal use, including patient selection and combination strategy, remains unknown. Moreover, there is an imbalance between the number of drugs with diverse mechanisms of action and the limited number of paediatric patients available to be enrolled in early-phase trials, so prioritisation and a strategy are essential. While PARP inhibitors targeting homologous recombination-deficient tumours have been used primarily in the treatment of adult cancers with BRCA1/2 mutations, BRCA1/2 mutations occur infrequently in childhood tumours, and therefore, a specific response hypothesis is required. Combinations with targeted radiotherapy, ATR inhibitors, or antibody drug conjugates with DNA topoisomerase I inhibitor-related warheads warrant evaluation. Additional monotherapy trials of PARP inhibitors with the same mechanism of action are not recommended. PARP1-specific inhibitors and PARP inhibitors with very good central nervous system penetration also deserve evaluation. ATR, ATM, DNA-PK, CHK1, WEE1, DNA polymerase theta and PKMYT1 inhibitors are early in paediatric development. There should be an overall coordinated strategy for their development. Therefore, an academia/industry consensus of the relevant biomarkers will be established and a focused meeting on ATR inhibitors (as proof of principle) held. CHK1 inhibitors have demonstrated activity in desmoplastic small round cell tumours and have a potential role in the treatment of other paediatric malignancies, such as neuroblastoma and Ewing sarcoma. Access to CHK1 inhibitors for paediatric clinical trials is a high priority. The three key elements in evaluating these inhibitors in children are (1) innovative trial design (design driven by a clear hypothesis with the intent to further investigate responders and non-responders with detailed retrospective molecular analyses to generate a revised or new hypothesis); (2) biomarker selection and (3) rational combination therapy, which is limited by overlapping toxicity. To maximally benefit children with cancer, investigators should work collaboratively to learn the lessons from the past and apply them to future studies. Plans should be based on the relevant biology, with a focus on simultaneous and parallel research in preclinical and clinical settings, and an overall integrated and collaborative strategy.

Progressive metastatic infantile fibrosarcoma with multiple acquired mutations

Infantile fibrosarcoma is the most common soft tissue sarcoma in children under the age of 1 year and is defined molecularly by NTRK fusion proteins. This tumor is known to be locally invasive; however, metastasis are rare. The NTRK fusion acts as a driver for tumor formation which can be targeted by first and second generation NTRK inhibitors. While NTRK gatekeeper mutations have been well described as mechanisms of resistance to these agents, alternative pathway acquired mutations are rare. Here we report the case of a patient with infantile sarcoma treated with chemotherapy and NTRK inhibition that developed metastatic, progressive disease with multiple acquired mutations, including TP53, SUFU, and an NTRK F617L gatekeeper mutation. Alterations in pathways of SUFU and TP53 have been widely described in the literature in other tumors, however, not yet in infantile fibrosarcoma. While most patients have a sustained response to TRK inhibitors, a subset will go on to develop mechanisms of resistance that have implications for clinical management, such as in our patient. We hypothesize this constellation of mutations contributed to the patient's aggressive clinical course. Taken together, we report the first case of infantile fibrosarcoma with ETV6::NTRK3 and acquired SUFU, TP53, and NTRK F617L gatekeeper mutation along with detailed clinical course and management. Our report highlights the importance of genomic profiling in recurrent infantile fibrosarcoma to reveal actionable mutations, such as gatekeeper mutations, that can improve patient outcomes.

Malignant Progression of an Ancestral Bone Marrow Clone Harboring a CIC-NUTM2A Fusion in Isolated Myeloid Sarcoma

Myeloid sarcoma is a rare condition consisting of extramedullary myeloid blasts found in association with acute myeloid leukemia or, in the absence of bone marrow involvement. We identified an infant with isolated myeloid sarcoma whose bone marrow was negative for involvement by flow cytometry. Sequencing revealed the fusion oncogene CIC-NUTM2A and identified the sarcoma to be clonally evolved from the bone marrow, which carried the fusion despite the absence of pathology. Murine modeling confirmed the ability of the fusion to transform hematopoietic cells and identified receptor tyrosine kinase (RTK) signaling activation consistent with disruption of the CIC transcriptional repressor. These findings extend the definition of CIC-rearranged malignancies to include hematologic disease, provide insight into the mechanism of oncogenesis, and demonstrate the importance of molecular analysis and tracking of bone marrow involvement over the course of treatment in myeloid sarcoma, including patients that lack flow cytometric evidence of leukemia at diagnosis.

IMPLICATIONS

This study illustrates molecular involvement of phenotypically normal bone marrow in myeloid sarcoma, which has significant implications in clinical care. Further, it extends the definition of CIC-rearrangements to include hematologic malignancies and shows evidence of RTK activation that may be exploited therapeutically in cancer(s) driven by these fusions.

Paediatric Strategy Forum for medicinal product development in mitogen-activated protein kinase pathway inhibitors: ACCELERATE in collaboration with the European Medicines Agency with participation of the Food and Drug Administration

As the mitogen-activated protein kinase (MAPK) signalling pathway is activated in many paediatric cancers, it is an important therapeutic target. Currently, a range of targeted MAPK pathway inhibitors are being developed in adults. However, MAPK signals through many cascades and feedback loops and perturbing the MAPK pathway may have substantial influence on other pathways as well as normal development. In view of these issues, the ninth Paediatric Strategy Forum focused on MAPK inhibitors. Development of MAPK pathway inhibitors to date has been predominantly driven by adult indications such as malignant melanoma. However, these inhibitors may also target unmet needs in paediatric low-grade gliomas, high-grade gliomas, Langerhans cell histiocytosis, juvenile myelomonocytic leukaemia and several other paediatric conditions. Although MAPK inhibitors have demonstrated activity in paediatric cancer, the response rates and duration of responses needs improvement and better documentation. The rapid development and evaluation of combination approaches, based on a deep understanding of biology, is required to optimise responses and to avoid paradoxical tumour growth and other unintended consequences including severe toxicity. Better inhibitors with higher central nervous systempenetration for primary brain tumours and cancers with a propensity for central nervous system metastases need to be studied to determine if they are more effective than agents currently being used, and the optimum duration of therapy with MAPK inhibition needs to be determined. Systematic and coordinated clinical investigations to inform future treatment strategies with MAPK inhibitors, rather than use outside of clinical trials, are needed to fully assess the risks and benefits of these single agents and combination strategies in both front-line and in the refractory/relapse settings. Platform trials could address the investigation of multiple similar products and combinations. Accelerating the introduction of MAPK inhibitors into front-line paediatric studies is a priority, as is ensuring that these studies generate data appropriate for scientific and regulatory purposes. Early discussions with regulators are crucial, particularly if external controls are considered as randomised control trials in small patient populations can be challenging. Functional end-points specific to the populations in which they are studied, such as visual acuity, motor and neuro psychological function are important, as these outcomes are often more reflective of benefit for lower grade tumours (such as paediatric low-grade glioma and plexiform neurofibroma) and should be included in initial study designs for paediatric low-grade glioma. Early prospective discussions and agreements with regulators are necessary. Long-term follow-up of patients receiving MAPK inhibitors is crucial in view of their prolonged administration and the important involvement of this pathway in normal development. Further rational development, with a detailed understanding of biology of this class of products, is crucial to ensure they provide optimal benefit while minimising toxicity to children and adolescents with cancer.

Rationale and design of ON-TRK: a novel prospective non-interventional study in patients with TRK fusion cancer treated with larotrectinib

BACKGROUND

Tropomyosin receptor kinase (TRK) fusion proteins resulting from neurotrophic tyrosine receptor kinase (NTRK) gene fusions are rare primary oncogenic drivers in a wide array of tumors. Larotrectinib is a first-in-class, highly selective, central nervous system-active TRK inhibitor approved by the US Food and Drug Administration (FDA), European Medicines Agency (EMA), and over 40 countries for the treatment of TRK fusion solid tumors in adult and pediatric patients. Due to the rarity of TRK fusion cancer, larotrectinib was granted accelerated approval based on a relatively small number of patients enrolled in three early phase trials. ON-TRK aims to evaluate the safety profile of larotrectinib in a broader population and over extended time periods.

METHODS

ON-TRK is a prospective, non-interventional, open-label, multicenter, multi-cohort, post-approval study in adult and pediatric patients with locally advanced or metastatic TRK fusion cancer treated with larotrectinib that will describe the safety and effectiveness of larotrectinib in real-world practice conditions. Adult patients will be grouped by tumor type and followed for at least 2 years. Patients < 18 years old will be enrolled under a 'pediatric' cohort regardless of tumor type and will be followed for 5 years to evaluate the risk of potential long-term adverse effects of larotrectinib on their growth and development. The effectiveness of larotrectinib in the overall study population as well as in patient subgroups will also be evaluated. Procedures avoided in patients with infantile fibrosarcoma (e.g., amputation) and the number of patients who were able to undergo surgery with a curative intent (excluding amputation) because of the use of larotrectinib will be described. Larotrectinib treatment patterns in real-world practice, including dosing and duration of treatment, will be described.

DISCUSSION

The FDA Accelerated Approval Program allows for earlier approval of and patient access to drugs that treat serious conditions and fill an unmet medical need. This study is designed to fulfill post-approval requirements set by the FDA as well as post-marketing requirements set forth by local regulatory bodies and is part of the risk management plan for the EMA.

STUDY REGISTRATION

This study is registered at ClinicalTrials.gov ( NCT04142437 ).

PROTOCOL VERSION

v2.5, 25 March 2021.

0500 Increased adherence to light therapy and psychosocial outcomes in adolescents and young adults with cancer

Introduction

Adolescent/young adult (AYA) oncology patients consistently report fatigue as one of the most distressing symptoms during treatment. Bright white light (BWL) has been demonstrated to improve the symptoms of cancer-related fatigue in adults, and our prior research demonstrated feasibility, acceptability, and preliminary efficacy of BWL in AYA with cancer. As part of the trial examining the feasibility and acceptability of BWL in AYA, we explored whether adherence affected patient outcomes in the BWL group.

Methods

Twenty-seven participants were randomized to receive BWL using LiteBook® (retrofitted with adherence monitors) for 30 minutes upon waking daily for eight weeks. Study team members met with patients weekly for the duration of the intervention to download adherence data from the monitors, administer questionnaires, and discuss barriers to adherence if necessary. Participants completed mood, quality of life, and fatigue measures at every other research visit (5 times over the duration of the study).

Results

Adherence was characterized by total number of days that participants used the light device while on study. Multivariate regression was used to examine the predictive relationship between adherence and patient outcomes. Adherence significantly predicted parent-reported physical functioning [β=1.45, p= 0.0079], emotional functioning [β=0.87, p=0.0137], and total health-related quality of life [β= 0.76, p= 0.0218]. Adherence did not predict any of the self-reported patient outcomes.

Conclusion

BWL is a promising treatment to improve cancer-related fatigue in AYA, and adherence is essential to treatment success. Although adherence did not predict any participant self-reported outcomes, participants with better adherence had improved parent-reported emotional and physical functioning and overall quality of life. Individually tailored interventions, including sleep hygiene psychoeducation and motivational interviewing, may be used to increase adherence to light therapy to improve patient outcomes. Measures to monitor and foster adherence should be included in future light therapy trials.

Support (If Any)

This research was funded and supported by ALSAC.

The myogenesis program drives clonal selection and drug resistance in rhabdomyosarcoma

Rhabdomyosarcoma (RMS) is a pediatric cancer with features of skeletal muscle; patients with unresectable or metastatic RMS fare poorly due to high rates of disease recurrence. Here, we use single-cell and single-nucleus RNA sequencing to show that RMS tumors recapitulate the spectrum of embryonal myogenesis. Using matched patient samples from a clinical trial and orthotopic patient-derived xenografts (O-PDXs), we show that chemotherapy eliminates the most proliferative component with features of myoblasts within embryonal RMS; after treatment, the immature population with features of paraxial mesoderm expands to reconstitute the developmental hierarchy of the original tumor. We discovered that this paraxial mesoderm population is dependent on EGFR signaling and is sensitive to EGFR inhibitors. Taken together, these data serve as a proof of concept that targeting each developmental state in embryonal RMS is an effective strategy for improving outcomes by preventing disease recurrence.

Antigen cross-presentation in young tumor-bearing hosts promotes CD8+ T cell terminal differentiation

The immune system undergoes a progressive functional remodeling with age. Understanding how age bias shapes antitumor immunity is essential in designing effective immunotherapies, especially for pediatric patients. Here, we explore antitumor CD8⁺ T cell responses generated in young (prepubescent) and adult (presenescent) mice. Using an MHCI-deficient tumor model, we observed that tumor-reactive CD8⁺ T cells expanded in young tumor-bearing (TB) mice acquired a terminally differentiated phenotype characterized by overexpression of inhibitory receptors and the transcription factor Tox1. Furthermore, tumor-infiltrating CD8⁺ T cells from young tumors yielded a poor cytokine response compared with CD8⁺ T cells infiltrating adult tumors. Young migratory dendritic cells (migDCs) from the draining lymph nodes (dLNs), and mononuclear phagocytic cells (MPCs) infiltrating young tumors, were more competent in capturing and cross-presenting tumor antigen, leading to enhanced priming of CD8⁺ T cells in dLNs and their subsequent terminal differentiation in the tumors. Single-cell transcriptional profiling of tumor-infiltrating MPCs demonstrated that young MPCs are polarized toward an inflammatory, effector phenotype. Consistent with our observations in young versus adult TB mice, analysis of immune infiltrates from pediatric solid tumors showed a correlation between tumor-infiltrating CD8⁺ T cells with an exhaustion phenotype and the frequency of PD-L1-expressing monocytes/macrophages. Collectively, these data indicate that a young tissue microenvironment contributes to the generation of an immune response skewed toward a less pliable terminal effector state, thus narrowing the window for immunotherapeutic interventions.

Improved Outcome in Children With Newly Diagnosed High-Risk Neuroblastoma Treated With Chemoimmunotherapy: Updated Results of a Phase II Study Using hu14.18K322A

PURPOSE

We evaluated whether combining a humanized antidisialoganglioside monoclonal antibody (hu14.18K322A) throughout therapy improves early response and outcomes in children with newly diagnosed high-risk neuroblastoma.

PATIENTS AND METHODS

We conducted a prospective, single-arm, three-stage, phase II clinical trial. Six cycles of induction chemotherapy were coadministered with hu14.18K322A, granulocyte-macrophage colony-stimulating factor (GM-CSF), and low-dose interleukin-2 (IL-2). The consolidation regimen included busulfan and melphalan. When available, an additional cycle of parent-derived natural killer cells with hu14.18K322A was administered during consolidation (n = 31). Radiation therapy was administered at the end of consolidation. Postconsolidation treatment included hu14.18K322A, GM-CSF, IL-2, and isotretinoin. Early response was assessed after the first two cycles of induction therapy. End-of-induction response, event-free survival (EFS), and overall survival (OS) were evaluated.

RESULTS

Sixty-four patients received hu14.18K322A with induction chemotherapy. This regimen was well tolerated, with continuous infusion narcotics. Partial responses (PRs) or better after the first two chemoimmunotherapy cycles occurred in 42 of 63 evaluable patients (66.7%; 95% CI, 55.0 to 78.3). Primary tumor volume decreased by a median of 75% (range, 100% [complete disappearance]-5% growth). Median peak hu14.18K322A serum levels in cycle one correlated with early response to therapy (P = .0154, one-sided t-test). Sixty of 62 patients (97%) had an end-of-induction partial response or better. No patients experienced progressive disease during induction. The 3-year EFS was 73.7% (95% CI, 60.0 to 83.4), and the OS was 86.0% (95% CI, 73.8 to 92.8), respectively.

CONCLUSION

Adding hu14.18K322A to induction chemotherapy improved early objective responses, significantly reduced tumor volumes in most patients, improved end-of-induction response rates, and yielded an encouraging 3-year EFS. These results, if validated in a larger study, may be practice changing.

Paediatric Strategy Forum for medicinal product development of chimeric antigen receptor T-cells in children and adolescents with cancer: ACCELERATE in collaboration with the European Medicines Agency with participation of the Food and Drug Administration

The seventh multi-stakeholder Paediatric Strategy Forum focused on chimeric antigen receptor (CAR) T-cells for children and adolescents with cancer. The development of CAR T-cells for patients with haematological malignancies, especially B-cell precursor acute lymphoblastic leukaemia (BCP-ALL), has been spectacular. However, currently, there are scientific, clinical and logistical challenges for use of CAR T-cells in BCP-ALL and other paediatric malignancies, particularly in acute myeloid leukaemia (AML), lymphomas and solid tumours. The aims of the Forum were to summarise the current landscape of CAR T-cell therapy development in paediatrics, too identify current challenges and future directions, with consideration of other immune effector modalities and ascertain the best strategies to accelerate their development and availability to children. Although the effect is of limited duration in about half of the patients, anti-CD19 CAR T-cells produce high response rates in relapsed/refractory BCP-ALL and this has highlighted previously unknown mechanisms of relapse. CAR T-cell treatment as first- or second-line therapy could also potentially benefit patients whose disease has high-risk features associated with relapse and failure of conventional therapies. Identifying patients with very early and early relapse in whom CAR T-cell therapy may replace haematopoietic stem cell transplantation and be definitive therapy versus those in whom it provides a more effective bridge to haematopoietic stem cell transplantation is a very high priority. Development of approaches to improve persistence, either by improving T cell fitness or using more humanised/fully humanised products and co-targeting of multiple antigens to prevent antigen escape, could potentially further optimise therapy. Many differences exist between paediatric B-cell non-Hodgkin lymphomas (B-NHL) and BCP-ALL. In view of the very small patient numbers with relapsed lymphoma, careful prioritisation is needed to evaluate CAR T-cells in children with Burkitt lymphoma, primary mediastinal B cell lymphoma and other NHL subtypes. Combination trials of alternative targets to CD19 (CD20 or CD22) should also be explored as a priority to improve efficacy in this population. Development of CD30 CAR T-cell immunotherapy strategies in patients with relapsed/refractory Hodgkin lymphoma will likely be most efficiently accomplished by joint paediatric and adult trials. CAR T-cell approaches are early in development for AML and T-ALL, given the unique challenges of successful immunotherapy actualisation in these diseases. At this time, CD33 and CD123 appear to be the most universal targets in AML and CD7 in T-ALL. The results of ongoing or planned first-in-human studies are required to facilitate further understanding. There are promising early results in solid tumours, particularly with GD2 targeting cell therapies in neuroblastoma and central nervous system gliomas that represent significant unmet clinical needs. Further understanding of biology is critical to success. The comparative benefits of autologous versus allogeneic CAR T-cells, T-cells engineered with T cell receptors T-cells engineered with T cell receptor fusion constructs, CAR Natural Killer (NK)-cell products, bispecific T-cell engager antibodies and antibody-drug conjugates require evaluation in paediatric malignancies. Early and proactive academia and multi-company engagement are mandatory to advance cellular immunotherapies in paediatric oncology. Regulatory advice should be sought very early in the design and preparation of clinical trials of innovative medicines, for which regulatory approval may ultimately be sought. Aligning strategic, scientific, regulatory, health technology and funding requirements from the inception of a clinical trial is especially important as these are very expensive therapies. The model for drug development for cell therapy in paediatric oncology could also involve a 'later stage handoff' to industry after early development in academic hands. Finally, and very importantly, strategies must evolve to ensure appropriate ease of access for children who need and could potentially benefit from these therapies.

Light Therapy for QoL/Depression in AYA With Cancer: A Randomized Trial

OBJECTIVE

Secondary outcomes from a published feasibility and acceptability trial were examined to explore the effect of bright white light (BWL) on quality of life (QoL) and depressive symptoms compared to dim red light (DRL) control in adolescents and young adults (AYAs) receiving cancer-directed therapy.

METHODS

Fifty-one AYAs (12-22 years, 51% male) newly diagnosed with cancer were randomized to receive 8 weeks of BWL (n = 26) or DRL (n = 25). The CDI-2 (total score, negative mood/physical symptoms, interpersonal problems, ineffectiveness, and negative self-esteem) and parent- and self-report PedsQL (total score and subscales of physical, emotional, social, and school QoL) were completed at multiple timepoints.

RESULTS

BWL produced improvements in self-reported total depression (d = -.64; 95% confidence interval [CI] = -1.26, -0.01), negative self-esteem (d = -.80; 95% CI = -1.43, -.14), negative mood/physical symptoms (d = -.73; 95% CI = -1.36, -0.08), ineffectiveness (d = -.43; 95% CI = -1.04, .19), total self-reported QoL (d = .41; 95% CI = -.16, .96), emotional (d = .78; 95% CI = .19, 1.37), school functioning (d = .48; 95% CI = -.09, 1.04), and parent-reported school functioning (d = .66; 95% CI = 0.02, 1.33). BWL reported a greater rate of improvement than DRL for total depression (β = .49, p < .05) and self-esteem (β = .44, p < .05), and parent-reported school functioning (β = -1.68, p < .05).

CONCLUSIONS

BWL improved QoL and depressive symptoms for AYAs with cancer. These findings will inform larger randomized controlled trials.

Synovial Sarcoma in Children, Adolescents, and Young Adults: A Report From the Children's Oncology Group ARST0332 Study

PURPOSE

Synovial sarcoma (SS) is the second most common malignant soft tissue tumor in children. ARST0332 evaluated a risk-based treatment strategy for young patients with soft tissue sarcoma designed to limit therapy for low-risk (LR) disease and to test neoadjuvant chemoradiotherapy for unresected higher-risk disease.

METHODS

Newly diagnosed patients with SS age < 30 years were assigned to four treatment arms based on disease features: A (surgery only), B (55.8 Gy radiotherapy [RT]), C (ifosfamide and doxorubicin [ID] chemotherapy plus 55.8 Gy RT), and D (neoadjuvant ID and 45 Gy RT, then surgery and RT boost based on margins followed by adjuvant ID). Patients treated in Arms A and B were considered LR, arms C and D without metastases as intermediate-risk (IR), and those with metastases as high-risk (HR).

RESULTS

Of the 146 patients with SS enrolled, 138 were eligible and evaluable: LR (46), IR (71), and HR (21). Tumors were 80% extremity, 70% > 5 cm, 70% high-grade, 62% invasive, 95% deep, and 15% metastatic. Treatment was on arm A (29.7%), B (3.6%), C (16.7%), and D (50%). There were no toxic deaths and four unexpected grade 4 adverse events. By risk group, at a median follow-up of 6.8 years, estimated 5-year event-free survival was LR 82%, IR 70%, and HR 8%, and overall survival was LR 98%, IR 89%, and HR 13%. After accounting for the features that defined risk category, none of the other patient or disease characteristics (age, sex, tumor site, tumor invasiveness, and depth) improved the risk stratification model.

CONCLUSION

The risk-based treatment strategy used in ARST0332 produced favorable outcomes in patients with nonmetastatic SS relative to historical controls despite using RT less frequently and at lower doses. The outcome for metastatic SS remains unsatisfactory and new therapies are urgently needed.

Abstract 642: Genomes for Kids: Comprehensive DNA and RNA sequencing defining the scope of actionable mutations in pediatric cancer

Clinical genomic studies of pediatric cancer have primarily focused on specific tumor types or high-risk disease. In the Genomes for Kids study (NCT02530658) we used a three-platform sequencing approach, including whole genome (WGS), whole exome (WES) and RNA sequencing, to examine tumor and paired germline genomes from prospectively identified children with cancer. The goal of the study was to assess the potential of comprehensive next generation sequencing to elucidate the molecular mechanisms underlying tumor formation and investigate the potential of this information to influence clinical decision-making.The cohort, with a median age of 6 yrs, range 0 - 26 yrs, included 301 patients with newly diagnosed (85%) or relapsed/refractory (15%) cancers, unselected for tumor type or stage. Patients with hematologic malignancies accounted for 41% of cases, 31% had CNS tumors, and 28% had other non-CNS solid tumors. This cohort also included 18 patients with very rare tumor types, defined here as occurring in less than 2 cases per million person per year.Two hundred fifty three patients (84%) had sufficient tumor for three-platform sequencing and all 301 had adequate paired germline samples. Following analysis, 86% of patients harbored diagnostic (53%), prognostic (57%), therapeutically relevant (25%), and/or cancer predisposing (18%) variants. The inclusion of WGS enabled detection of oncogenic gene fusions, as well as 22 cases in which oncogenes were activated through enhancer hijacking, a particularly frequent occurrence in hematologic malignancies. In addition, WGS effectively detected clinically relevant small intragenic deletions (15% of tumors) and a variety of mutational signatures, which were not detectable through analysis of whole exome data. Evaluation of 56 pathogenic germline variants in the context of paired tumor sequence data helped establish the disease relevance of several genes that are not typically associated with the cancer type in question, providing critical insights on a case-by-case basis. Examples include a pathogenic germline variant in MUTYH in a patient with retinoblastoma whose tumor exhibited a mutation signature associated with reactive oxygen species indicative of loss of MUTYH function; and conversely, a likely pathogenic variant in PMS2 in a rare brain cancer, which did not exhibit a mutation signature associated with microsatellite instability. This study successfully demonstrated the power of this three-platform approach to interrogate and interpret the full range of genomic variants across newly diagnosed as well as relapsed/refractory pediatric cancers. As a result of these findings, we have incorporated this three-platform approach into our routine real-time clinical service at St. Jude Children's Hospital.

Citation Format: David A. Wheeler, Scott Newman, Joy Nakitandwe, Chimene A. Kesserwan, Elizabeth M. Azzato, Michael C. Rusch, Sheila Shurtleff, Armita Bahrami, Brent Orr, Jeffery M. Klco, Dale J. Hedges, Kayla V. Hamilton, Scott G. Foy, Michael N. Edmonson, Andrew Thrasher, Jiali Gu, Lynn W. Harrison, Lu Wang, Roya Mostafavi, Manish Kubal, Jamie Maciaszek, Michael Clay, Annastasia Ouma, Antonina Silkov, Yanling Liu, Zhaojie Zhang, Yu Liu, Samuel W. Brady, Xin Zhou, Mark Wilkinson, Delaram Rahbarinia, Jay Knight, Jian Wang, Charles G. Mullighan, Rose B. McGee, Emily A. Quinn, Elsie L. Gerhardt, Leslie M. Taylor, Regina Nuccio, Jessica M. Valdez, Stacy J. Hines-Dowell, Alberto Pappo, Giles Robinson, Liza-Marie Johnson, Ching-Hon Pui, David W. Ellison, James R. Downing, Jinghui Zhang, Kim E. Nichols. Genomes for Kids: Comprehensive DNA and RNA sequencing defining the scope of actionable mutations in pediatric cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 642.

Feasibility and Acceptability of Light Therapy to Reduce Fatigue in Adolescents and Young Adults Receiving Cancer-Directed Therapy

OBJECTIVE/BACKGROUND

Fatigue is one of the most consistent and distressing symptoms reported by adolescent/young adult (AYA) oncology patients. Bright white light (BWL) is used to treat fatigue in adult oncology but has not been explored in AYA oncology patients. The purpose of the current study was to determine the feasibility and acceptability of BWL for AYA who were receiving cancer-directed therapy.

PARTICIPANTS

51 AYA patients with newly diagnosed solid tumors, including lymphoma.

METHODS

Participants were randomized to dim red light (DRL, n = 25) or BWL (n = 26) from devices retrofitted with adherence monitors for 30 minutes upon awakening daily for 8 weeks. Side effects were assessed via modified Systematic Assessment for Treatment-Emergent Effects (SAFTEE). Participants completed the PedsQL Multidimensional Fatigue Scale.

RESULTS

Of patients approached, 73% consented and participated. Mean adherence was 57% of days on study with 30.68 average daily minutes of usage. BWL did not cause more extreme treatment-emergent effects over DRL. Patients in the BWL group demonstrated significant improvement on all fatigue outcomes by both self-report and parent proxy report, which was not observed in the DRL group.

CONCLUSIONS

This is the first study to evaluate the feasibility and acceptability of light therapy to reduce fatigue in AYA patients receiving cancer-directed therapy. These findings demonstrate the feasibility and acceptability of the intervention and provide preliminary evidence of the potential benefits of BWL, which warrants further study in a confirmatory efficacy trial.ClinicalTrials.gov Identifier Number: NCT02429063.

Cutaneous melanoma in children and adolescents: The EXPeRT/PARTNER diagnostic and therapeutic recommendations

Cutaneous melanoma is rare in children and, like other very rare pediatric tumors, it suffers from a shortage of knowledge and clinical expertise. The clinical management of pediatric melanoma is often challenging. Its clinical and pathological diagnosis may be difficult, and there is no standard treatment. In the absence of specific treatment guidelines, young patients are generally treated following the same principle as for adults, but concern remains about their access to clinical trials and new drugs, which have been shown to dramatically change the natural history of advanced melanoma. This paper presents the internationally recognized recommendations for the diagnosis and treatment of children and adolescents with cutaneous melanoma, established by the European Cooperative Study Group for Pediatric Rare Tumors (EXPeRT) within the EU-funded project called PARTNER (Paediatric Rare Tumours Network - European Registry). Main recommendations for melanoma are to discuss pediatric patients in multidisciplinary teams that include both pediatric oncologists and specialists in adult melanoma; to enroll patients in prospective trials, if available; to collect data in national-international databases; and to develop an effective international collaboration between pediatric and adult melanoma groups in order to facilitate the transfer of potentially effective new agents from the adult to the pediatric setting.

Developmental vascular malformations in EPAS1 gain-of-function syndrome

Mutations in EPAS1, encoding hypoxia-inducible factor-2α (HIF-2α), were previously identified in a syndrome of multiple paragangliomas, somatostatinoma, and polycythemia. HIF-2α, when dimerized with HIF-1β, acts as an angiogenic transcription factor. Patients referred to the NIH for new, recurrent, and/or metastatic paraganglioma or pheochromocytoma were confirmed for EPAS1 gain-of-function mutation; imaging was evaluated for vascular malformations. We evaluated the Epas1^A529V transgenic syndrome mouse model, corresponding to the mutation initially detected in the patients (EPAS1^A530V), for vascular malformations via intravital 2-photon microscopy of meningeal vessels, terminal vascular perfusion with Microfil silicate polymer and subsequent intact ex vivo 14T MRI and micro-CT, and histologic sectioning and staining of the brain and identified pathologies. Further, we evaluated retinas from corresponding developmental time points (P7, P14, and P21) and the adult dura via immunofluorescent labeling of vessels and confocal imaging. We identified a spectrum of vascular malformations in all 9 syndromic patients and in all our tested mutant mice. Patient vessels had higher variant allele frequency than adjacent normal tissue. Veins of the murine retina and intracranial dura failed to regress normally at the expected developmental time points. These findings add vascular malformation as a new clinical feature of EPAS1 gain-of-function syndrome.

We discovered vascular malformations due to failure of developmental vascular regression in patients with EPAS1 gain-of-function mutation syndrome and the corresponding transgenic mouse model.

A newborn with a large NTRK fusion positive infantile fibrosarcoma successfully treated with larotrectinib

Infantile fibrosarcoma (IFS) is a rare pediatric cancer that typically presents early in life. Surgical resection is commonly curative; however, resection is sometimes not possible requiring additional multimodal treatment. IFS commonly harbors a fusion in one of the neurotrophic receptor tyrosine kinase (NTRK) genes. Larotrectinib, a highly selective inhibitor of tropomyosin receptor kinase (TRK), has been shown to be well tolerated and effective in children as young as 1-month old. We report a case of IFS in a newborn treated with larotrectinib. The patient experienced a rapid clinical and radiographic response demonstrating the potential to treat newborns with larotrectinib.

Abstract 6149: An innovative integrated cloud-based data portal for orthotopic patient-derived xenografts (O-PDX) available through the Childhood Solid Tumor Network (CSTN)

Despite making significant advances over the past 25 years in our understanding of the most common adult solid tumors, much less is known about childhood solid tumors. We have previously described a protocol to produce orthotopic patient-derived xenografts (O-PDX) at diagnosis, recurrence and autopsy. These O-PDX models provide both in vivo and in vitro systems to study mechanisms of disease origin, tumor progression and preclinical testing. Here, we present an innovative cloud-based all-in-one data portal to explore various biological features of these pediatric O-PDX models. The vast diversity of the collected childhood solid tumors is represented in 166 O-PDX models, consisting of 21 diagnoses including Neuroblastoma, Osteosarcoma, Rhabdomyosarcoma, and a large number of rare solid tumors including Ewing Sarcoma, Desmoplastic Small Cell Round Tumor, Fibrosarcoma, High Grade Sarcoma, Liposarcoma, Retinoblastoma, Rhabdoid Tumor and Synovial Sarcoma. The O-PDX models have been characterized and compared to the original patient tumor using various methods and assays including histology, electron microscopy, short tandem repeat DNA profiling, chemical compound screening as well as genomic sequencing (whole genome sequencing, whole exome sequencing, and RNA Sequencing) and clonal analysis to determine the clonal population in the O-PDX. Somatic genetic mutations as well as clonal architecture is retained in the majority of O-PDX tumors. The data on O-PDX models can now be visualized and compared in our web-based CSTN data portal on St Jude Cloud (www.stjude.cloud). The user-friendly interface allows both gene and sample level search and visualization. For genomics variations, the presence or absence of a particular variant can be observed through interactive heatmaps. In addition to genomic and transcriptomic profiles, some of these models have extensive epigenomic and proteomic profiling which are integrated into the portal. We have also included chemical sensitivity heatmaps and dose response curves for common oncology drugs using primary cultures of the O-PDXs and cell lines. Importantly, the raw genomics sequencing data is also available from St Jude Cloud, following a straightforward application and approval process for access. In summary, the integration of data from multi-omics and beyond at the CSTN data portal provides a rich resource for both academic and industrial research community to find the appropriate models to advance the knowledge and therapeutic solutions to the catastrophic childhood solid tumors. *co-first #co-corresponding

Citation Format: Asa Karlstrom, Ti-Cheng Chang, Darrell Gentry, Xin Zhou, Elizabeth Stewart, Brittney Gordon, Sara M. Federico, Rachel Brennan, Michael R. Clay, Sharon Frase, Armita Bahrami, Xiang Chen, Anang A. Shelat, Nathaniel R. Twarog, Daniel Alford, Anthony Woodard, Edgar Sioson, Irina McGuire, Cynthia Williams, Nedra Robison, Brandon McMahan, Ashok K. Boddu, Swapnali Mohite, Kirby Birch, Clay McLeod, Michael Rusch, Alberto Pappo, Keith Perry, Gang Wu, Ed Suh, Michael A. Dyer. An innovative integrated cloud-based data portal for orthotopic patient-derived xenografts (O-PDX) available through the Childhood Solid Tumor Network (CSTN) [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 6149.

Recent advances in understanding and managing pediatric rhabdomyosarcoma

Rhabdomyosarcoma (RMS) is a high-grade malignant neoplasm, with a morphologic appearance mimicking that of developing skeletal muscle. Over the last 30 years, patient outcomes have improved with the incorporation of multimodal therapies, including chemotherapy, radiation therapy, and surgery. The overall cure rates exceed 70%, with patients who have low-, intermediate-, and high-risk disease experiencing long-term survival rates of >90%, 70%, and <30%, respectively. Historically, RMS was classified according to histology; however, recent advances have revealed new molecular subgroups that allow us to more accurately identify high-, intermediate-, and low-risk disease. In this review, we discuss recent advances made in understanding RMS tumor biology and propose how this understanding can drive a new classification system that can guide clinical approaches for treatment de-escalation in patients with expected favorable outcomes and escalation for those with expected poor outcomes.

IGF-1R/mTOR Targeted Therapy for Ewing Sarcoma: A Meta-Analysis of Five IGF-1R-Related Trials Matched to Proteomic and Radiologic Predictive Biomarkers

Background : Ten to fourteen percent of Ewing sarcoma (ES) study participants treated nationwide with IGF-1 receptor (IGF-1R)-targeted antibodies achieved tumor regression. Despite this success, low response rates and short response durations (approximately 7-weeks) have slowed the development of this therapy. Methods: We performed a meta-analysis of five phase-1b/2 ES-oriented trials that evaluated the anticancer activity of IGF-1R antibodies +/− mTOR inhibitors (mTORi). Our meta-analysis provided a head-to-head comparison of the clinical benefits of IGF-1R antibodies vs. the IGF-1R/mTOR-targeted combination. Available pretreatment clinical samples were semi-quantitatively scored using immunohistochemistry to detect proteins in the IGF-1R/PI3K/AKT/mTOR pathway linked to clinical response. Early PET/CT imaging, obtained within the first 2 weeks (median 10 days), were examined to determine if reduced FDG avidity was predictive of progression-free survival (PFS). Results: Among 56 ES patients treated at MD Anderson Cancer Center (MDACC) with IGF-1R antibodies, our analysis revealed a significant ~two-fold improvement in PFS that favored a combination of IGF-1R/mTORi therapy (1.6 vs. 3.3-months, p = 0.042). Low pIGF-1R in the pretreatment specimens was associated with treatment response. Reduced total-lesion glycolysis more accurately predicted the IGF-1R response than other previously reported radiological biomarkers. Conclusion: Synergistic drug combinations, and newly identified proteomic or radiological biomarkers of IGF-1R response, may be incorporated into future IGF-1R-related trials to improve the response rate in ES patients.

XAF1 as a modifier of p53 function and cancer susceptibility

Cancer risk is highly variable in carriers of the common TP53-R337H founder allele, possibly due to the influence of modifier genes. Whole-genome sequencing identified a variant in the tumor suppressor XAF1 (E134*/Glu134Ter/rs146752602) in a subset of R337H carriers. Haplotype-defining variants were verified in 203 patients with cancer, 582 relatives, and 42,438 newborns. The compound mutant haplotype was enriched in patients with cancer, conferring risk for sarcoma (P = 0.003) and subsequent malignancies (P = 0.006). Functional analyses demonstrated that wild-type XAF1 enhances transactivation of wild-type and hypomorphic TP53 variants, whereas XAF1-E134* is markedly attenuated in this activity. We propose that cosegregation of XAF1-E134* and TP53-R337H mutations leads to a more aggressive cancer phenotype than TP53-R337H alone, with implications for genetic counseling and clinical management of hypomorphic TP53 mutant carriers.

Antigen-cross presentation promotes development of terminally differentiated CD8 T cells in young individuals

Cancer immunotherapeutic approaches that rely on endogenous T cell responses have shown limited success in children, a pattern attributed to the low mutational burden of pediatric tumors. Here, we report that CD8 T cells isolated from a diverse set of pediatric solid tumors are enriched for an antigen-experienced phenotype. The limited ability of immune checkpoint blockade therapy (ICBT) to trigger anti-tumor responses in children, despite the presence of activated CD8 T cells, prompted us to explore alternative underlying mechanisms restricting anti-tumor responses. Using a novel mouse tumor model that expresses a well-characterized epitope coupled to an mCherry marker, we identified antigen cross-presentation by tumor infiltrating myeloid cells as a key regulator of CD8 T cell effector function in tumors. Strikingly, age-related changes in the TME resulted in a skewing of the CD8 T cell effector fate toward a terminally differentiated state in young tumor-bearing mice. Profiling of tumor infiltrating antigen presenting cells by scRNAseq revealed a proinflammatory M1 macrophage polarization in young tumors but a predominant M2 “wound healing” response in adult tumors. Consistent with our mouse findings, analysis of immune infiltrates from human pediatric solid tumors revealed a strong correlation between the expression of PDL1 on myeloid cells and enrichment of tumor-associated CD8 T cells with an exhaustion phenotype. Collectively, these data indicate that the “young” microenvironment of an actively developing tissue/individual contributes to the generation of an immune response skewed towards a terminally differentiated state with limited plasticity, thus narrowing the window for immunotherapeutic interventions.

Clinical manifestations of Pacak-Zhuang syndrome in a male pediatric patient

We report an index case of a male patient who presented with all clinical manifestations of Pacak-Zhuang syndrome, including early-age polycythemia, multiple pheochromocytomas/paragangliomas, duodenal somatostatinoma, and ocular findings. Sequencing analysis detected an EPAS1 mutation in all tumors tested, but not in the germline.

MYCN amplification and ATRX mutations are incompatible in neuroblastoma

Aggressive cancers often have activating mutations in growth-controlling oncogenes and inactivating mutations in tumor-suppressor genes. In neuroblastoma, amplification of the MYCN oncogene and inactivation of the ATRX tumor-suppressor gene correlate with high-risk disease and poor prognosis. Here we show that ATRX mutations and MYCN amplification are mutually exclusive across all ages and stages in neuroblastoma. Using human cell lines and mouse models, we found that elevated MYCN expression and ATRX mutations are incompatible. Elevated MYCN levels promote metabolic reprogramming, mitochondrial dysfunction, reactive-oxygen species generation, and DNA-replicative stress. The combination of replicative stress caused by defects in the ATRX-histone chaperone complex, and that induced by MYCN-mediated metabolic reprogramming, leads to synthetic lethality. Therefore, ATRX and MYCN represent an unusual example, where inactivation of a tumor-suppressor gene and activation of an oncogene are incompatible. This synthetic lethality may eventually be exploited to improve outcomes for patients with high-risk neuroblastoma.

Primary bone sarcoma with BCOR internal tandem duplication

BCOR internal tandem duplications (ITDs) and rearrangements are implicated in the oncogenesis of a subset of undifferentiated sarcomas. To date, BCOR ITD sarcomas have been exclusively found in non-appendicular infantile soft tissues, whereas BCOR-rearranged sarcomas occur in both bones and soft tissues affecting a wider patient age range. Little is known about patient outcome in BCOR ITD sarcomas. We present a BCOR-expressing, primary bone, undifferentiated sarcoma case involving an adolescent male's left tibia that, unexpectedly, harbored a BCOR ITD instead of a BCOR rearrangement. Furthermore, the patient achieved a partial histologic response after receiving a Ewing sarcoma chemotherapy regimen. Our case expands the clinical spectrum of BCOR ITD sarcomas and suggests that childhood and adult BCOR-expressing sarcomas with an undifferentiated histology should be considered for both BCOR rearrangement and ITD screening. Accurate BCOR mutation identification in undifferentiated sarcomas is essential to define their clinical spectrum and to develop effective management strategies.

Pembrolizumab in paediatric patients with advanced melanoma or a PD-L1-positive, advanced, relapsed, or refractory solid tumour or lymphoma (KEYNOTE-051): interim analysis of an open-label, single-arm, phase 1-2 trial

BACKGROUND

Pembrolizumab is approved for the treatment of advanced cancer in adults; however, no information is available on safety and efficacy in paediatric patients. We aimed to establish the recommended phase 2 dose of pembrolizumab and its safety and antitumour activity in advanced paediatric cancer.

METHODS

KEYNOTE-051 is an ongoing phase 1-2 open-label trial. In this interim analysis, children aged 6 months to 17 years were recruited at 30 hospitals located in Australia, Brazil, Canada, France, Germany, Israel, Italy, South Korea, Sweden, the UK, and the USA. Patients with melanoma or a centrally confirmed, PD-L1-positive, relapsed or refractory solid tumour or lymphoma, and a Lansky Play/Karnofsky Performance status score of 50 or higher, received intravenous pembrolizumab at an initial dose of 2 mg/kg every 3 weeks. Pharmacokinetics and dose-limiting toxicities were used to establish the recommended phase 2 dose, and the safety and antitumour activity of this dose were assessed. Primary endpoints were determination of dose-limiting toxicities at the maximum administered dose, safety and tolerability, and the proportion of patients with objective response to pembrolizumab for each tumour type according to the Response Evaluation Criteria in Solid Tumours version 1.1 or the International Neuroblastoma Response Criteria. Safety and efficacy were assessed in all treated patients who received at least one dose of pembrolizumab. Separate reporting of the cohort of patients with relapsed or refractory classical Hodgkin lymphoma was a post-hoc decision. The data cutoff for this interim analysis was Sept 3, 2018. This trial is still enrolling patients and is registered with ClinicalTrials.gov, number NCT02332668.

FINDINGS

Of 863 patients screened between March 23, 2015, and Sept 3, 2018, 796 had tumours that were evaluable for PD-L1 expression (278 [35%] were PD-L1-positive); 155 eligible patients were enrolled and 154 had at least one dose of pembrolizumab. The median age of the enrolled patients was 13 years (IQR 8-15). Median follow-up was 8·6 months (IQR 2·5-16·4). No dose-limiting toxicities were reported in phase 1, and pembrolizumab plasma concentrations were consistent with those previously reported in adults; the recommended phase 2 dose was therefore established as 2 mg/kg every 3 weeks. Of the 154 patients treated, 69 (45%) experienced grade 3-5 adverse events, most commonly anaemia in 14 (9%) patients and decreased lymphocyte count in nine (6%) patients. 13 (8%) of the 154 patients had grade 3-5 treatment-related adverse events, most commonly decreased lymphocyte count in three (2%) patients and anaemia in two (1%) patients. 14 (9%) patients had serious treatment-related adverse events, most commonly pyrexia (four [3%]), and hypertension and pleural effusion (two [1%] each). Four patients (3%) discontinued treatment because of treatment-related adverse events, and two (1%) died (one due to pulmonary oedema and one due to pleural effusion and pneumonitis). Of 15 patients with relapsed or refractory Hodgkin lymphoma, two had complete and seven had partial responses; thus, nine patients achieved an objective response (60·0%; 95% CI 32·3-83·7). Of 136 patients with solid tumours and other lymphomas, eight had partial responses (two patients each with adrenocortical carcinoma and mesothelioma, and one patient each with malignant ganglioglioma, epithelioid sarcoma, lymphoepithelial carcinoma, and malignant rhabdoid tumour); the proportion of patients with an objective response was 5·9% (95% CI 2·6-11·3).

INTERPRETATION

Pembrolizumab was well tolerated and showed encouraging antitumour activity in paediatric patients with relapsed or refractory Hodgkin lymphoma, consistent with experience in adult patients. Pembrolizumab had low antitumour activity in the majority of paediatric tumour types, and responses were observed in only a few rare PD-L1-positive tumour types, suggesting that PD-L1 expression alone is not sufficient as a biomarker for the selection of paediatric patients who are likely to respond to PD-1 checkpoint inhibitors. Final results of KEYNOTE-051, expected by September, 2022, with the possibility for extension, will report further on the activity of pembrolizumab in Hodgkin lymphoma, microsatellite instability-high tumours, and melanoma.

FUNDING

Merck Sharp & Dohme, a subsidiary of Merck & Co.

Abstract 731: Clinical genome sequencing uncovers potentially targetable truncations and fusions of MAP3K8 in spitzoid and other melanomas

Most melanomas arising in children and adolescents are of the spitzoid subtype. Unlike conventional melanomas in adults, spitzoid tumors are driven by fusions of kinase genes such as ALK, NTRK1/3, MET, RET and ROS1. However, in approximately 50% of cases, no oncogenic driver has been established. This raises the possibility of an, as yet, undescribed oncogene in such tumors.

Clinical whole genome and transcriptome (RNA-Seq) sequencing detected a novel fusion of MAP3K8 in a spitzoid melanoma from an adolescent patient. The fusion preserved the kinase domain of MAP3K8 - a serine threonine kinase that activates MEK/ERK downstream - but replaced the autoinhibitory final exon with an unrelated gene, GNG2. MAP3K8 is a proposed oncogene in breast, ovarian, squamous cell carcinoma and lung cancer and its high expression has been shown to cause resistance to BRAF inhibitors through a MEK-dependent mechanism in melanoma cells (Johannessen et al. 2010 Nature 468:968-72). As the patient had exhausted other therapeutic options, we treated him with the MEK inhibitor, trametinib, and observed a transient response. He later relapsed, and further clinical sequencing showed the MAP3K8-GNG2 fusion had increased in genomic copy number and expression - potentially explaining the acquired resistance to trametinib.

We subsequently screened a cohort of 49 pediatric melanomas with spitzoid features by RNA-Seq, fluorescence in situ hybridization and immunohistochemistry and found that MAP3K8 fusions and truncations were the most common genetic event, supplying the missing kinase driver for 33% of samples. All rearrangements preserved MAP3K8 exons 1-8 but replaced the autoinhibitory final exon with unrelated genetic or intergenic sequence. Strikingly, MAP3K8 rearrangements were mutually exclusive of other known driver mutations such as ALK fusions, further implicating MAP3K8 as a driver oncogene. Transformation assays using NIH 3T3 cells confirmed that the truncated form of MAP3K8 was oncogenic.

Finally, we screened over 11,000 TCGA RNA-Seq samples, and identified seven adult melanomas with analogous MAP3K8 disruptions (1.5% of SKCM samples). Similar to their pediatric counterparts, all seven tumors lacked any other kinase driver mutation. Thus, MAP3K8 rearrangements drive a subset of adult melanomas and these tumors may also be amenable to MEK inhibition. Our experience highlights the need for genome-wide clinical sequencing as MAP3K8 is not covered by popular targeted gene panels.

Citation Format: Scott Newman, Liying Fan, Allison Pribnow, Antonina Silkov, Stephen V. Rice, Seungjae Lee, Ying Shao, Bridget Shaner, Heather Mulder, Joy Nakitandwe, Sheila Shurtleff, Elizabeth Azzato, Gang Wu, Xin Zhou, Raymond Barnhill, John Easton, Kim E. Nichols, David W. Ellison, Downing R. James, Alberto Pappo, Philip M. Potter, Jinghui Zhang, Armita Bahrami. Clinical genome sequencing uncovers potentially targetable truncations and fusions of MAP3K8 in spitzoid and other melanomas [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 731.

OR02-1 DNA Methylation Profiling in Pediatric Adrenocortical Tumors Reveals Distinct Methylation Signatures with Prognostic Significance: A Report from the International Pediatric Adrenocortical Tumor Registry

Pediatric adrenocortical tumors (ACTs) are heterogeneous and have a poor prognosis. Overall survival is around 60%. In pediatric ACT that is managed only with surgery, features associated with adverse outcome include age greater than 3 years, non-functioning tumors, and metastatic (Stage IV) or residual tumor after surgery (Stage III). These factors individually do not account for most treatment failures, however. As current histopathologic classification systems are hindered by poor reproducibility and lack of predictive value, new prognostic markers are critically needed. In adults, methylation profiling can distinguish benign from malignant ACT, but similar data on pediatric ACT have not been reported. We performed DNA methylation profiling (MethylationEPIC BeadChip Array) on 52 pediatric ACTs and 13 normal pediatric adrenocortical tissue samples. The median age of 38 girls and 14 boys was 2.8 years (range, 0.3-17). ACTs were histologically classified as carcinoma (n=29), adenoma (n=10), and indeterminate (n=13). Overall survival was used as a primary endpoint. Unsupervised analysis of the 20,000 most variably methylated probes segregated cases into two distinct subgroups (designated A1 and A2). Differentially methylated genes (q-value<0.05) between A1 and A2 groups included those associated with IGF-, mTOR, WNT, and HGF/cMET signaling pathways. Other genes commonly mutated in pediatric malignancies (DICER1, EZH2,EGFR, PTEN, RB1, TERT, SF1, and MEN1) were also differentially methylated. Normal adrenal cortex samples segregated with the A2 group. The A1 subgroup had unique copy number changes, and recurrent global hypomethylation of chromosomes 4, 13, and 18. Moreover, the A1 group was significantly associated with higher frequency of CTNNB1 mutations (OR = 4.2, p = 0.03), lower frequency of TP53 mutations (p = 0.04), and use of chemotherapy (OR = 9.7, p = 0.0007). Methylation subgroups were not significantly associated with sex, histopathologic classification, disease stage, or ATRX status. In a univariable analysis, vascular invasion (HR=6.2, p=0.02), tumor weight (HR=10.9, p=0.001), tumor size (HR=11.3, p=0.002), tumor volume (cm³, HR=8.53, p=0.008), diffuse necrosis (HR=9.21, p=0.03), proliferative index by Ki-67 immunohistochemical staining (HR=7.1, p=0.02), disease stage III/IV (HR = 9.8, p = 0.03), age > 4 years (HR = 16.8, p = 0.008) and A1 methylation group (HR 7.7, p=0.0011) were each significantly correlated with overall survival. A1 subgroup remained significantly associated with overall survival in a series of models that adjusted for features including: clinical diagnosis, histopathologic characteristics, Ki67 index, and advanced stage. Methylation profiling provides prognostic significance that is independent of most current predictive variables, and in the future, may serve as a powerful biomarker in the prognostication of pediatric ACT.

The role of routine imaging in pediatric cutaneous melanoma

BACKGROUND

Optimal imaging for children with pediatric malignant melanoma (MM) is unknown.

METHODS

We reviewed clinical and imaging findings of patients with American Joint Commission on Cancer (AJCC) stage IIC-IV MM treated on our institutional MEL06 trial. All patients had baseline brain magnetic resonance imaging/computed tomography (MRI/CT), positron emission tomography/computed tomography (PET/CT), CT chest, abdomen, and pelvis (CTCAP). Patients on stratum A (PEG-interferon, where PEG is pegylated; AJCC IIC, IIIA, IIIB; n = 16) had imaging every 6 months; stratum B1 (PEG-interferon and temozolomide; unresectable measurable disease, metastatic, or recurrent; n = 2) had PET/CT scans every 2 months and brain imaging studies every 4 months; stratum B2 patients (PEG-interferon and temozolomide; unresectable nonmeasurable, metastatic, or recurrent, n = 3) had imaging every 4 months. Off-therapy imaging was done every 6 months for 3 years.

RESULTS

There were 21 patients (11 females, 11 spitzoid, median age 14 years, head/neck [6], trunk [7], extremities [8]). Patients with spitzoid melanoma underwent 236 imaging studies in total (86 PET/CT, 81 CTCAP, 11 CT chest, 10 CT brain, 48 MRI brain) at a median cost per patient of $32,718. Thirteen studies (5.8%) had findings that led to two biopsies (one positive). For conventional MM, 162 studies (61 PET/CT, 57 CTCAP, 8 CT chest, 7 CT brain, and 29 MRI brain) were performed with a median cost per patient of $23,420. Twenty (14%) had findings leading to six biopsies (four positive). At 6.3 years (range 0.4-9.2), 17 patients remain disease-free.

CONCLUSION

Children with spitzoid melanoma require minimal imaging at diagnosis and follow-up. Patients with conventional MM should be imaged according to adult guidelines.

Identification of Therapeutic Targets in Rhabdomyosarcoma through Integrated Genomic, Epigenomic, and Proteomic Analyses

Personalized cancer therapy targeting somatic mutations in patient tumors is increasingly being incorporated into practice. Other therapeutic vulnerabilities resulting from changes in gene expression due to tumor specific epigenetic perturbations are progressively being recognized. These genomic and epigenomic changes are ultimately manifest in the tumor proteome and phosphoproteome. We integrated transcriptomic, epigenomic, and proteomic/phosphoproteomic data to elucidate the cellular origins and therapeutic vulnerabilities of rhabdomyosarcoma (RMS). We discovered that alveolar RMS occurs further along the developmental program than embryonal RMS. We also identified deregulation of the RAS/MEK/ERK/CDK4/6, G₂/M, and unfolded protein response pathways through our integrated analysis. Comprehensive preclinical testing revealed that targeting the WEE1 kinase in the G₂/M pathway is the most effective approach in vivo for high-risk RMS.

Xenotransplantation of pre-pubertal ovarian cortex and prevention of follicle depletion with anti-Müllerian hormone (AMH)

OBJECTIVE

To determine whether recombinant AMH (rAMH) could prevent post-transplant follicular depletion by acting on the stemness markers Oct-4, Sox2, and NANOG.

MATERIALS AND METHODS

This was an experimental study where 12 ovariectomized nude mice were xenotransplanted with vitrified/warmed ovarian cortex obtained from a pre-pubertal girl and Alzet pumps delivering rAMH, or placebo (control), were inserted intra-abdominally. Previously vitrified/warmed ovarian cortex fragments were transplanted after 7 days and then harvested after 14 days from pump placement. We performed real-time RT-PCR analyses, ELISA for AMH, FSH, and estradiol, histologic measurement of ovarian follicles, and immunohistochemistry for Ki67 and TUNEL. The main outcome measures were serum levels and tissue expression of the parameters under investigation and follicle count.

RESULTS

Serum AMH, FSH, and estradiol reflected post-ovariectomy profiles and were mildly influenced by rAMH administration. Ovarian cortex expression of AMH, AMH-R2, VEGF, GDF9, Oct-4, and Sox2 was lower in rAMH mice than in controls, while NANOG was upregulated. There was a non-significant decrease in primordial follicles after vitrification-warming, and xenotransplantation further decreased this number. There were lower cell replication and depressed apoptosis in the rAMH group.

CONCLUSIONS

Administration of recombinant AMH in the peri-transplant period did not protect the initial follicular depletion but decreased apoptosis and cellular activation and regulated stem cell markers' tissue expression. These results aid our understanding of the inhibitory effects of AMH on follicular development and show the benefit of administering exogenous AMH at the time of pre-pubertal ovarian cortex transplant to protect the follicles from pre-activation and premature depletion.

Histology, fusion status, and outcome in metastatic rhabdomyosarcoma: A report from the Children's Oncology Group

BACKGROUND

Distinguishing alveolar rhabdomyosarcoma (ARMS) from embryonal rhabdomyosarcoma (ERMS) has historically been of prognostic and therapeutic importance. However, classification has been complicated by shifting histologic criteria required for an ARMS diagnosis. Children's Oncology Group (COG) studies after IRS-IV, which included the height of this diagnostic shift, showed both an increased number of ARMS and an increase in the proportion of fusion-negative ARMS. Following diagnostic standardization and histologic re-review of ARMS cases enrolled during this era, analysis of low-risk (D9602) and intermediate-risk (D9803) rhabdomyosarcoma (RMS) studies showed that fusion status rather than histology best predicts prognosis for patients with RMS. This analysis remains to be completed for patients with high-risk RMS.

PROCEDURE

We re-reviewed cases on high-risk COG studies D9802 and ARST0431 with an enrollment diagnosis of ARMS. We compared the event-free survival (EFS) and overall survival by histology, PAX-FOXO1 fusion, and clinical risk factors (Oberlin score) for patients with metastatic RMS using the log-rank test.

RESULTS

Histology re-review resulted in reclassification as ERMS for 12% of D9802 cases and 5% of ARST0431 cases. Fusion-negative RMS had a superior EFS to fusion-positive RMS; however, poorer outcome for metastatic RMS was most related to clinical risk factors including age, primary site, and number of metastatic sites.

CONCLUSIONS

In contrast to low- or intermediate-risk RMS, in metastatic RMS, clinical risk factors have the most impact on patient outcome. PAX-FOXO1 fusion is more common in patients with a high Oberlin score, but fusion status is not an independent biomarker of prognosis.

Phase II study of ipilimumab in adolescents with unresectable stage III or IV malignant melanoma

BACKGROUND

Ipilimumab is approved for the treatment of advanced melanoma in adults; however, little information on the efficacy and safety of ipilimumab in younger patients is available.

METHODS

Patients aged 12 to <18 years with previously treated or untreated, unresectable stage III or IV malignant melanoma received ipilimumab 3 or 10 mg/kg every 3 weeks. Primary end-points were 1-year overall survival and safety.

RESULTS

Over a period of 3.5 years, 12 patients received ipilimumab at either 3 mg/kg (n = 4) or 10 mg/kg (n = 8). The median number of ipilimumab doses was four for 3 mg/kg and three for 10 mg/kg. At 1 year, three of four patients on 3 mg/kg and five of eight patients on 10 mg/kg were alive. Two patients on 10 mg/kg had partial response, and one on 3 mg/kg had stable disease. One patient had durable partial response at 3 years without further treatment, at time of this report. There was one grade 3/4 immune-mediated adverse reaction with 3 mg/kg and five with 10 mg/kg. There were no treatment-related deaths. The study was stopped due to slow accrual.

CONCLUSIONS

At >1 year follow-up, ipilimumab demonstrated activity in melanoma patients aged 12 to <18 years, with a similar safety profile as that seen in adults. Our trial highlights the difficulties of enrolling younger patients with rare diseases in clinical trials for treatments that are approved in adults, suggesting adolescents with cancer types occurring predominantly in adults should be considered for inclusion in adult trials of promising new drugs.

CLINICAL TRIAL REGISTRATION

NCT01696045.

Nonrhabdomyosarcoma soft tissue sarcoma (NRSTS) in pediatric and young adult patients: Results from a prospective study using limited-margin radiotherapy

BACKGROUND

Indications for and delivery of adjuvant therapies for pediatric nonrhabdomyosarcoma soft tissue sarcoma (NRSTS) have been derived largely from adult studies; therefore, significant concern remains regarding radiation exposure to normal tissue. The authors report long-term treatment outcomes and toxicities for pediatric and young adult patients with high-grade NRSTS who were treated on a prospective trial using limited-margin radiotherapy.

METHODS

Sixty-two patients (ages 3-22 years) with predominantly high-grade NRSTS requiring radiation were treated on a phase 2 institutional study of conformal external-beam radiotherapy and/or brachytherapy using a 1.5-cm to 2-cm anatomically constrained margin. The estimated cumulative incidence of local failure, Gray's method estimated cumulative incidence of local failure, Kaplan-Meier method estimated survival, competing-risk regression model determined predictors of disease outcome, and toxicity was reported according to CTCAE v2.0.

RESULTS

At a median follow-up of 5.1 years (range, 0.2-10.9 years), 9 patients had experienced local failure. The 5-year overall cumulative incidence of local failure was 14.8% (95% confidence interval [CI], 7.2%-25%), and all but 1 local failure occurred outside the highest-dose irradiation volume. The 5-year Kaplan-Meier estimates for event-free and overall survival were 49.3% (95% CI, 36.3%-61.1%) and 67.9% (95% CI, 54.2%-78.3%), respectively. Multivariable analysis indicated that younger age was the only independent predictor of local recurrence (P = .004). The 5-year cumulative incidence of grade 3 or 4 late toxicity was 15% (95% CI, 7.2%-25.3%).

CONCLUSIONS

The delivery of limited-margin radiotherapy using conformal external-beam radiotherapy or brachytherapy provides a high rate of local tumor control without an increase in marginal failures and with acceptable treatment-related morbidity. Cancer 2017;123:4419-29. © 2017 American Cancer Society.

Feasibility and functional outcomes of children and adolescents undergoing preoperative chemotherapy prior to a limb-sparing procedure or amputation

BACKGROUND

Survivors of lower extremity (LE) malignancies experience functional deficits.

PURPOSE

The purpose of this prospective clinical trial was to determine feasibility and functional outcomes of adding pre-habilitation during the 10-12 week period prior to a planned surgery to remove the tumor in children and adolescents with a LE sarcoma.

DESIGN

Pilot study.

SETTING

St. Jude Children's Research Hospital (SJCRH).

PATIENTS

Participants included 14 individuals between the ages of 8 and 20 years who were diagnosed with a LE sarcoma. Participant outcomes were compared to a control group of 35 individuals treated for osteosarcoma that obtained the same functional assessments but no pre-habilitation.

INTERVENTION

The intervention group received strengthening exercises and mobility training 3 times per week for 30-60 minutes for 10-12 weeks preoperatively.

MEASUREMENTS

Participants completed the Functional Mobility Assessment (FMA) and measures of strength and range of motion (ROM) of bilateral lower extremities (BLEs) at baseline, after 10-12 weeks of preoperative PT, and at 20-22 weeks.

RESULTS

Twelve participants completed at least 50% of their schedule pre-habilitative sessions. The intervention group scored significantly better on the FMA than the control group at weeks 20-22 (35.6 vs. 25.7, p .0267). No significant difference was found in ROM or strength.

LIMITATIONS

Due to this study being a pilot study, the sample size was small. Therefore, we cannot infer generalizability.

CONCLUSIONS

Findings suggest that those diagnosed with a LE malignancy awaiting a limb sparing procedure or amputation participate in at least 50% of scheduled PT sessions and benefit from them.

Infantile Fibrosarcoma With NTRK3-ETV6 Fusion Successfully Treated With the Tropomyosin-Related Kinase Inhibitor LOXO-101

Infantile fibrosarcoma (IFS) is a rare pediatric cancer typically presenting in the first 2 years of life. Surgical resection is usually curative and chemotherapy is active against gross residual disease. However, when recurrences occur, therapeutic options are limited. We report a case of refractory IFS with constitutive activation of the tropomyosin-related kinase (TRK) signaling pathway from an ETS variant gene 6-neurotrophin 3 receptor gene (ETV6-NTRK3) gene fusion. The patient enrolled in a pediatric Phase 1 trial of LOXO-101, an experimental, highly selective inhibitor of TRK. The patient experienced a rapid, radiographic response, demonstrating the potential for LOXO-101 to provide benefit for IFS harboring NTRK gene fusions.

Abstract 2730: Association of TERT promoter mutations with telomerase expression in melanoma

Telomerase reverse transcriptase (TERT) promoter mutations occur at a high frequency in melanoma, but the functional consequences of these mutations in melanoma remain to be clarified. In a large study of melanoma samples by The Cancer Genome Atlas network, mRNA expression analysis using RNA sequencing data showed that only TERT promoter mutations at C228T were associated with high TERT expression levels. The effect of hotspot C250 or C242T/C243T tandem mutations on telomerase expression has not yet been determined. To assess telomerase expression levels in melanomas harboring C250 or C242T/C243T mutations, we used real-time quantitative reverse transcriptase polymerase chain reaction (RT-qPCR) in a sample set of pediatric melanocytic tumors for which the methylation status and the mutational profile of the TERT promoter were known. We previously showed that in a subset of melanoma, TERT expression is mediated epigenetically by promoter hypermethylation rather than by promoter point mutations. Formalin-fixed paraffin-embedded (FFPE) tissues from 10 metastatic melanomas, of which 8 harbored a hotspot TERT promoter mutation (5 C250T; 2 C228; 1 C242T/C243T) and 2 carried a hypermethylated wild-type TERT promoter were examined. For controls, 9 atypical Spitz tumors with a wild-type unmethylated TERT promoter were also studied. Total RNA was isolated from FFPE tumor tissues and converted to cDNA. TERT expression levels were determined by RT-qPCR by using the TaqMan® Gene Expression Assay and normalized with GAPDH as the endogenous control. In the atypical Spitz tumor samples, TERT mRNA expression was undetectable or negligible. In contrast, TERT expression in all melanoma samples was elevated, ranging from 3- to 71-fold (median, 25-fold) when compared to an atypical Spitz tumor as a reference. Our data support that in melanoma, TERT promoter hotspot C250 and C242T/C243T mutations, similar to C228T mutations, correlate with TERT overexpression and that C250 and C242T/C243T mutations likely contribute biologically to tumorigenesis in melanoma.

Citation Format: Seungjae Lee, Patricia Opresko, Alberto Pappo, John Kirkwood, Armita Bahrami. Association of TERT promoter mutations with telomerase expression in melanoma. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 2730.

Feasibility of Pegylated Interferon in Children and Young Adults With Resected High-Risk Melanoma

BACKGROUND

Pegylated interferon α-2b (IFN α-2b) improves disease-free survival in adults with resected stage III melanoma. We conducted a study to determine the feasibility and safety of incorporating pegylated IFN α-2b as adjuvant therapy in the treatment of children and adolescents with high-risk melanoma. Pharmacokinetic studies of IFN α-2b and neuropsychological and quality of life (OL) assessments were performed.

PATIENT AND METHODS

Eligible patients with resected American Joint Committee on Cancer Stage IIC, IIIA, and IIIB cutaneous melanoma received nonpegylated IFN α-2b 20 million units/m(2) /day intravenously 5 days per week for 4 weeks (induction) followed by pegylated IFN α-2b 1 μg/kg/dose weekly subcutaneously (SQ) for 48 weeks (maintenance).

RESULTS

Twenty-three patients (15 females, median age 10 years) were enrolled. All patients completed induction therapy; five patients did not complete maintenance therapy either because of recurrent disease (n = 2) or toxicity (n = 3). The most common grade 3 and 4 toxicities of pegylated IFN α-2b were neutropenia (35%) and elevated liver transaminases (17%). The median nonpegylated IFN α-2b AUC0-∞ (5,026 pcg⋅hr/ml) was similar to adults. The median pegylated IFN α-2b exposure (48,480 pcg⋅hr/ml) was greater than the cumulative weekly exposure for nonpegylated IFN α-2b administered SQ three times per week (TIW). Validated measures demonstrated an improvement in QOL scores and no decline in psychological functioning over the course of therapy.

CONCLUSIONS

Pegylated IFN α-2b 1 μg/kg/dose SQ weekly as maintenance therapy in children and adolescents with high-risk melanoma is feasible with tolerable toxicity and appears to yield higher exposures than nonpegylated IFN α-2b administered SQ TIW.

Tumor Necrosis in Pediatric Osteosarcoma: Impact of Modern Therapies

Tumor necrosis following preoperative chemotherapy in patients with osteosarcoma is a predictor of overall survival. With modern therapies, 45% of patients are expected to achieve more than 90% tumor necrosis. Investigators at the authors’ center, however, increasingly noted that patients were experiencing inferior necrosis responses. A retrospective study of treated patients at the center was undertaken to examine this. The purpose of this study was to determine (1) whether the number of patients with favorable histological responses had changed over time and (2) whether the percentage of patients with favorable responses was similar to published outcomes. Chart reviews were performed on patients treated from 1993 to 2003 according to the Pediatric Oncology Group 9351, regimen A protocol. Twenty-one patients met all eligibility requirements; 52% of patients had more than 90% necrosis. No correlation existed between degree of necrosis and year of treatment (r = 0.06; P = .8). Patients with osteosarcoma treated at the authors’ institution have comparable tumor necrosis responses to published outcomes, and no change occurred over time. This study stresses the importance of rigorous retrospective reviews before implementing treatment changes.