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Membrane protein leucine–rich repeat containing 15 (LRRC15) is known to be expressed in several solid tumors including osteosarcoma. ABBV-085, an antibody–drug conjugate against LRRC15, conjugated to monomethyl auristatin E (MMAE), was studied in osteosarcoma patient-derived xenografts (PDXs) by the Pediatric Preclinical Testing Consortium (PPTC). LRRC15 expression data were obtained from PPTC RNA-sequencing data for the PDX models. The TARGET database was mined for LRRC15 expression in human osteosarcoma. Protein expression was confirmed via IHC in three PDX models. Seven osteosarcoma PDX models (OS1, OS9, OS33, OS34, OS42, OS55, and OS60) with varying LRRC15 gene expression were studied. ABBV-085 was administered at 3 mg/kg (OS33), 6 mg/kg (all seven PDXs), and 12 mg/kg (OS60) weekly for 4 consecutive weeks via intraperitoneal injection. Control cohorts included vehicle and an isotype MMAE-linked antibody. Tumor volumes and responses were reported using PPTC statistical analysis. OS1, OS33, OS42, OS55, and OS60 had high LRRC15 expression while OS9 and OS34 had low LRRC15 expression. ABBV-085 inhibited tumor growth in six of seven PDX models as compared with vehicle control and significantly improved event-free survival in five of seven models as compared with isotype controls. Two models showed maintained complete responses while all others showed progressive disease. Response correlated with LRRC15 expression. ABBV-085’s antitumor activity against osteosarcoma PDX suggests LRRC15 may be a rational target for pursuing clinical trials in patients with this disease.

Purpose Pediatric patients with rhabdomyosarcoma (RMS) are treated with multimodal therapy, often with radiation therapy (RT) as part of local therapy. We report on the efficacy and patterns of failure after proton beam therapy (PBT) for RMS. Methods and Materials Between January 2006 and February 2017, patients with RMS were enrolled in a prospective institutional review board–approved registry protocol for pediatric patients undergoing PBT. Demographics, clinical characteristics, and treatment related outcomes were reviewed. Results Ninety-four RMS patients were treated with a combination of chemotherapy (CT) and PBT. The majority of patients had head and neck (49%) and genitourinary (30%) primaries. Median tumor size was 4.1 cm (range, 1.0-16.5 cm); 33 patients (35%) had primary tumors >5 cm. Median cyclophosphamide equivalent dose was 14.4 g/m2 (range, 0-30.8 g/m2). Median time from CT initiation to RT initiation was 13 weeks (range, 1-58 weeks). With median follow-up of 4 years, 4-year overall survival (OS) was 71%, and 4-year progression-free survival (PFS) was 63%. Thirty patients (32%) experienced relapse (13% with local failure [LF]). Four-year local control (LC) was 85% overall; 4-year LC rates were 100% for low-risk, 85% for intermediate-risk, and 55% for high-risk patients (P = .02). Tumor size predicted LC (P = .007), with 7% versus 33% LF rate by tumor size (≤5 cm vs >5 cm). Delayed RT delivery (≥13 weeks from initiation of CT) predicted worse LC (P = .01). Increased tumor size predicted both inferior PFS (P = .02) and OS (P = .01). Delayed RT delivery predicted both inferior PFS (P = .04) and OS (P = .03). Conclusions PBT provides LC comparable to prior studies using photon RT. Inferior LC, PFS, and OS rates were observed for patients with larger tumors and those treated with delayed RT. This finding supports ongoing prospective efforts to dose-escalate treatment of tumors >5 cm; however, these data call into question the optimal timing of local therapy, particularly for patients treated with reduced-dose cyclophosphamide.

Background Strategies to optimize management in rhabdomyosarcoma (RMS) include risk stratification to assign therapy aiming to minimize treatment morbidity yet improve outcomes. This analysis evaluated the relationship between complete metabolic response (CMR) as assessed by 18 F-fluorodeoxyglucose positron emission tomography-computed tomography (FDG-PET) imaging and event-free survival (EFS) in intermediate-risk (IR) and high-risk (HR) RMS patients. Methods FDG-PET imaging characteristics, including assessment of CMR and maximum standard uptake values (SUVmax) of the primary tumor, were evaluated by central review. Institutional reports of SUVmax were used when SUVmax values could not be determined by central review. One hundred and thirty IR and 105 HR patients had FDG-PET scans submitted for central review or had SUVmax data available from institutional report at any time point. A Cox proportional hazards regression model was used to evaluate the relationship between these parameters and EFS. Results SUVmax at study entry did not correlate with EFS for IR (p = 0.32) or HR (p = 0.86) patients. Compared to patients who did not achieve a CMR, EFS was not superior for IR patients who achieved a CMR at weeks 4 (p = 0.66) or 15 (p = 0.46), nor for HR patients who achieved CMR at week 6 (p = 0.75) or 19 (p = 0.28). Change in SUVmax at week 4 (p = 0.21) or 15 (p = 0.91) for IR patients or at week 6 (p = 0.75) or 19 (p = 0.61) for HR patients did not correlate with EFS. Conclusion Based on these data, FDG-PET does not appear to predict EFS in IR or HR-RMS. It remains to be determined whether FDG-PET has a role in predicting survival outcomes in other RMS subpopulations.

The role for PET with fludeoxyglucose F 18 (18F-FDG PET)/computed tomography (CT) in the management of pediatric sarcomas continues to be controversial. The literature supports a role for PET/CT in the staging and surveillance of certain specific pediatric sarcoma subtypes; however, the data are less clear regarding whether PET/CT can be used as a biomarker for prognostication. Despite the interest in using this imaging modality in the management of pediatric sarcomas, most studies are limited by retrospective design and small sample size. Additional data are necessary to fully understand how best to use 18F-FDG PET/CT in pediatric sarcoma management.

The spectrum of adrenal masses in the pediatric population markedly differs from that in the adult population. Imaging plays a crucial role in detecting adrenal masses, differentiating malignant from benign lesions, recognizing extra-adrenal lesions in the suprarenal fossa, and directing further management. Ultrasound is the primary imaging modality of choice for the evaluation of adrenal masses in the neonatal period, whereas MRI or CT is used as a problem-solving tool. In older children, computed tomography or magnetic resonance imaging is often required after initial sonographic evaluation for further characterization of a lesion. Herein, we discuss the salient imaging features along with pathophysiology and clinical features of pediatric adrenal masses.

Background Despite advances in care, the 5 year overall survival for patients with relapsed and or metastatic sarcoma remains as low as

Rhabdomyosarcoma is the most common soft tissue sarcoma diagnosed in children and adolescents. Patients that are diagnosed with advanced or relapsed disease have exceptionally poor outcomes. The Children’s Oncology Group (COG) convened a rhabdomyosarcoma new agent task force in 2020 to systematically evaluate novel agents for inclusion in phase 2 or phase 3 clinical trials for patients diagnosed with rhabdomyosarcoma, following a similar effort for Ewing sarcoma. The task force was comprised of clinicians and basic scientists who collectively identified new agents for evaluation and prioritization in clinical trial testing. Here, we report the work of the task force including the framework upon which the decisions were rendered and review the top classes of agents that were discussed. Representative agents include poly-ADP-ribose polymerase (PARP) inhibitors in combination with cytotoxic agents, mitogen-activated protein kinase (MEK) inhibitors in combination with type 1 insulin-like growth factor receptor (IGFR1) inhibitors, histone deacetylase (HDAC) inhibitors, and novel cytotoxic agents.

The prognosis of pediatric patients who present with metastatic or recurrent sarcomas remains poor. In this review, we summarize the advances in the management of metastatic and relapsed pediatric sarcoma by highlighting recent and future clinical trials. Research into the identification of novel therapies for refractory pediatric sarcomas continues to advance. Outcomes have not improved in several decades underlying a need for improved understanding of the biology behind these tumors and the identification of novel therapeutic molecular targets that can be exploited pharmacologically. Multiple challenges remain for novel therapy in sarcomas such as the selection of effective targets, management of toxicities, and the tumor microenvironment. Many unique challenges remain in the treatment of patients with refractory pediatric sarcomas. Multiple strategies and targets are under investigation that hold promise.

The use of PET/computed tomography (CT) for the evaluation and management of children, adolescents, and young adults continues to expand. The principal tracer used is 18F-fluorodeoxyglucose and the principal indication is oncology, particularly musculoskeletal neoplasms. The purpose of this article is to review the common applications of PET/CT for imaging of musculoskeletal issues in pediatrics and to introduce the use of PET/CT for nononcologic issues, such as infectious/inflammatory disorders, and review the use of 18F-sodium fluoride in trauma and sports-related injuries.

Background Regorafenib is a small molecule multikinase inhibitor that inhibits multiple kinases including BRAF, KIT, PDGFRB, RAF, RET, and VEGFR1-3. Procedures The in vivo anticancer effects of regorafenib were assessed in a panel of six osteosarcoma models, three rhabdomyosarcoma models, and one Ewing sarcoma model. Results Regorafenib induced modest inhibition of tumor growth in the models evaluated. Conclusion The overall pattern of response to regorafenib appears similar to that of the kinase inhibitor sorafenib, with pronounced slowing of tumor growth in some models, limited to the period of agent administration, being the primary treatment effect.

Considerable debate remains regarding how best to incorporate 18F-FDG-PET/CT into clinical practice for pediatric sarcomas. Although there is a clear role for 18F-FDG-PET/CT in staging pediatric sarcoma, the value of 18F-FDG-PET/CT in prognostication for pediatric sarcomas remains unclear. In osteosarcoma, Ewing sarcoma, and rhabdomyosarcoma, 18F-FDG-PET/CT may be most useful in the identification of skeletal metastases, where the literature consistently suggests that it has improved sensitivity and specificity as compared to bone scintigraphy. The role of the imaging modality in the identification of pulmonary metastatic disease is less clear. Further controversy exists regarding the use of 18F-FDG-PET/CT in predicting outcome. Several studies, particularly in osteosarcoma, suggest changes in the maximal standardized uptake value (SUVmax) that can predict histologic response following neoadjuvant chemotherapy as well as overall outcome. Conversely, studies are conflicting regarding the use of 18F-FDG-PET/CT as a prognostic tool in Ewing sarcoma and rhabdomyosarcoma. The role of 18F-FDG-PET/CT in pediatric nonrhabdomyosarcoma soft tissue sarcomas is unknown at this time. Although most studies have been small and retrospective, in certain histologic subtypes, there is a clear role for the use of this imaging modality. Additional prospective and larger studies are needed to fully determine how best to incorporate 18F-FDG-PET/CT into treatment regimens for pediatric sarcomas in the future.

The pediatric preclinical testing program previously demonstrated activity of eribulin in osteosarcoma patient-derived xenograft (PDX) models. The phase 2 trial in patients with relapsed osteosarcoma failed to meet response endpoints. Eribulin was evaluated in the original and an expanded set of PDX models and tested at multiple dose levels and schedules to evaluate dose-response. Maximal response was observed at the highest dose, consistent with prior results. The alternative schedule generated similar responses. We demonstrate steep dose-response for eribulin in osteosarcoma PDX models, implying that any deviation from achievement of effective concentrations may have a significant impact on activity.

The prognosis for metastatic osteosarcoma (OS) is poor and has not changed in several decades. Therapeutic paradigms that target and exploit novel molecular pathways are desperately needed. Recent preclinical data suggests that modulation of the Fas/FasL pathway may offer benefit in the treatment of refractory osteosarcoma. Fas and FasL are complimentary receptor-ligand proteins. Fas is expressed in multiple tissues, whereas FasL is restricted to privilege organs, such as the lung. Fas expression has been shown to inversely correlate with the metastatic potential of OS cells; tumor cells which express high levels of Fas have decreased metastatic potential and the ones that reach the lung undergo cell death upon interaction with constitutive FasL in the lung. Agents such as gemcitabine and the HDAC inhibitor, entinostat/Syndax 275, have been shown to upregulate Fas expression on OS cells, potentially leading to decreased OS pulmonary metastasis and improved outcome. Clinical trials are in development to evaluate this combination as a potential treatment option for patients with refractory OS.

Purpose/objective(s) Bladder and prostate are unfavorable sites for rhabdomyosarcoma (B/P-RMS), and represent a challenging location for radiotherapy. Materials/methods Nineteen patients with B/P-RMS were enrolled on a prospective registry protocol (2008-2017) and treated with chemotherapy, proton beam therapy (PBT), and surgical resection (n = 8; 42%). Emphasis was given to treatment technique, disease-related outcomes, and toxicity associated with PBT. Results The majority of patients had bladder RMS (74%) of embryonal histology (95%), Group III (68%), and intermediate-risk disease by Children's Oncology Group (COG) risk stratification (89%). Seven patients (37%) had primary tumors >5 cm in size. All patients were treated according to COG protocols. With a median follow-up of 66.2 months, 5-year overall survival (OS) and progression-free survival (PFS) were 76%. Four patients (21%) experienced disease relapse, all presenting with local failure. The 5-year local control (LC) rate was 76%. Tumor size predicted LC, with 5-year LC for patients with >5 cm tumors being 43% versus 100% for those with ≤5 cm tumors (P = .006). Univariate analysis demonstrated an effect of tumor size on OS (tumor >5 cm, hazard ratio [HR] 17.7, P = .049) and PFS (HR 17.7, P = .049). Acute grade 2 toxicity was observed in two patients (11%, transient proctitis). Late grade 2+ toxicity was observed in three patients (16%; n = 1 grade 2 skeletal deformity; n = 3 transient grade 2 urinary incontinence; one patient experienced both). Conclusions PBT for B/P-RMS affords promising disease-related outcomes with an acceptable toxicity profile. Higher local failure rates were observed for larger tumors, supporting dose-escalation components of ongoing RMS clinical trials.

Background. Copanlisib is a pan-class I phosphoinositide 3-kinase (PI3K) inhibitor with activity against all four PI3K class I isoforms (PI3Kα, PI3Kβ, PI3Kγ, and PI3Kδ). Copanlisib was approved for use by the FDA in the treatment of refractory follicular lymphoma in 2017. Preclinical data have suggested that deregulation of the PI3K pathway is a key driver of multiple malignancies. The relevance of this pathway in osteosarcoma tumorigenesis remains a subject of debate, however, whole genome and RNA sequencing data have revealed several PI3K aberrations in osteosarcoma tumor samples. The in vivo effects of copanlisib were studied in the Pediatric Preclinical Testing Consortium osteosarcoma xenograft models. Methods. The in vivo anticancer effects of copanlisib were assessed in a panel of 6 osteosarcoma models (OS-2, OS-9, OS-31, OS-33, OS-36, and OS-60). Copanlisib was administered by oral gavage at a dose of 10 mg/kg/day, two days on and five days off, repeated weekly for 4 weeks. Time to event and tumor volume responses were defined and analyzed utilizing standard PPTC statistical methods. Results. Copanlisib was well tolerated in the models with minimal weight loss and no treatment related mortality as compared to controls. Copanlisib induced prolonged event-free survival (EFS) in 5/6 osteosarcoma models (p Citation Format: Douglas Harrison, Jonathan Gill, Pooja Hingorani, Michael Roth, Wendong Zhang, Beverly Teicher, Eric J. Earley, Stephen W. Erickson, Gregory Gatto, Raushan T. Kurmasheva, Peter J. Houghton, Malcolm A. Smith, Edward A. Kolb, Richard Gorlick. Evaluation of the pan-class I phosphoinositide 3-kinase (PI3K) inhibitor copanlisib in the Pediatric Preclinical Testing Consortium osteosarcoma in vivo models [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 LB252.

TPS11577 Background: Several sarcomas possess chromosomal translocations in FET family members ( FUS, EWSR1, and TAF15) responsible for cancer development. Sarcomas caused by FET family gene rearrangements include ES, desmoplastic round cell small tumors (DSRCT), myxoid liposarcoma (ML), and several others. Lysine specific demethylase 1 (LSD1) is a critical protein for sarcoma development and progression through its colocalization and/or association with several FET family oncogenic transcription factors. This suggests that pharmacologic inhibition of LSD1 may be a therapeutic strategy. Seclidemstat (SP-2577, Salarius Pharmaceuticals) is an oral, first-in-class, small molecule with reversible, noncompetitive inhibition of LSD1 (IC50: 25–50 nM). In vitro and in vivo data demonstrate seclidemstat, or analogs, modulate EWS/ETS transcriptional activity, down-regulating oncogene expression and up-regulating tumor-suppressor gene expression, leading to significant tumor growth inhibition in ES mouse xenograft studies. Seclidemstat has shown in in vitro ES cell lines near additivity efficacy when added to TC. In in vitro studies of other FET-translocated sarcomas, including ML (FUS/DDIT3 fusion) and clear cell sarcoma (EWS/ATF1 fusion), seclidemstat showed anti-proliferative activity. In an ongoing Phase 1 trial investigating single agent seclidemstat in advanced solid tumors (NCT03895684), three pts with metastatic FET-translocated sarcomas had a median progression-free survival of 5.7 months (range: 4.3–7.2) with a best response of stable disease despite having a median of 5 (range: 1–7) prior therapies. Methods: This dose expansion Phase 1 study (NCT03600649) assesses seclidemstat at 900 mg PO BID, the recommended Phase 2 dose, in two expansion cohorts: a single agent expansion in select sarcoma pts (n = 30) and a safety lead-in dose escalation and expansion (n = 24) of seclidemstat combined with TC in pts with ES. Pts must be ≥12 years old, have ECOG performance status of 0 or 1, with a life expectancy > 4 months. In the select sarcoma cohort, pts must have ML (n = 15) or other sarcomas with FET family translocations (n = 15) including DSRCT. One to 3 prior lines of therapy are allowed. In the ES combination cohort, up to 2 lines of prior therapy are allowed. Primary objective is safety/tolerability and secondary objective is efficacy. The trial is currently recruiting across 8 locations in the United States. Clinical trial information: NCT03600649.

11514 Background: Ewing sarcoma (ES), a rare bone and soft tissue sarcoma mainly of adolescents and young adults, is characterized by a chromosomal translocation resulting in a fusion oncoprotein. Lysine specific demethylase 1 (LSD1) has been shown to associate with the fusion oncoprotein and promote oncogenic transcriptional activity making LSD1 an attractive target for ES treatment. Seclidemstat is a novel, selective, reversible oral LSD1 inhibitor capable of inhibiting both LSD1’s catalytic and scaffolding functions. This is the first report of an LSD1 inhibitor in a Phase 1 trial focused exclusively on ES. Methods: SALA-002-EW16 is a Phase 1 trial of single agent seclidemstat in patients (pts) with relapsed or refractory (R/R) ES. This report describes the completed monotherapy dose escalation. Pts > 12 years received oral SP-2577 twice daily in 28-day cycles under fasting conditions at the assigned dose level. The primary objective was safety and tolerability. Secondary objectives include to determine maximum-tolerated dose (MTD), recommended Phase 2 dose (RP2D), preliminary efficacy, pharmacokinetics, and pharmacodynamics. Results: As of December 30, 2020, 27 pts with R/R ES were enrolled. Pts received escalating doses of SP-2577 at 75 (n = 1), 150 (n = 2), 300 (n = 4), 600 (n = 6), 900 (n = 8), or 1200 mg PO BID (n = 6). The median age was 25 years (range 15–68), 63% were male, and pts had received a median of 3 (range 2–12) prior systemic therapies. There were no treatment-related deaths. The most common ( > 5%) grade 3 treatment-related adverse events (TRAEs) were vomiting (15%), abdominal pain (11%), and hypokalemia (11%). One pt (4%) with grade 3 pancreatitis reported a grade 4 AE of elevated lipase. All remaining grade 3 TRAEs, including hematological TRAEs, were reported in only one pt each. Four pts discontinued study for an AE (weight loss, pancreatitis, vomiting, abdominal pain). Three pts had a dose reduction. The first cycle dose-limiting toxicities were gastrointestinal-related AEs observed in 2 pts at 1200 mg BID. Thus, the MTD/RP2D was established as 900 mg BID. Peak plasma concentrations occurred at a median of 4 hours (h) post-dose and median terminal half-life was 6 h; exposure was dose proportional through 900 mg BID. One pt at 600 mg BID achieved a reduction in target lesions starting at end of C2 with further target lesion tumor shrinkage through end of C4 and C6 (maximum 76% tumor shrinkage) with coincident new non-target lesion appearance at end of C2. Of pts evaluable for response at the end of C2 (12 pts), two additional pts (16.7%) at 600 mg BID and 900 mg BID had overall stable disease. Conclusions: Seclidemstat has a manageable safety profile with proof-of-concept preliminary activity in heavily pretreated pts with relapsed/refractory ES. These data support the planned Phase 2 expansion of seclidemstat as single agent and in combination with chemotherapy in ES and other sarcomas that share similar translocations. Clinical trial information: NCT03600649.

e15022 Background: Despite advances in care, the 5 year overall survival for patients with relapsed and or metastatic sarcoma remains as low as < 35%. Currently, there are no biomarkers available to assess disease status in patients with sarcomas and as such, disease surveillance remains only reliant on serial imaging which increases the risk of secondary malignancies and heightens patient anxiety. Methods: Here, we enumerated the cell surface vimentin (CSV+) CTCs in the blood of 92 sarcoma pediatric and adolescent and young adult (AYA) patients. Results: We discovered the CSV+CTC could serve as a possible biomarker of disease with sensitivity of 85.3% and specificity of 75%. Significantly, patients who were deemed to be CSV+ CTC positive were found to have a worse overall survival compared to those who were CSV+ CTC negative (773 days vs 2622 days). Addition of readily available genetic analyses improved the sensitivity in both diagnostic and prognostic tests. Conclusions: Our findings indicate that CSV+ CTCs have both diagnostic and prognostic value and can possibly serve as a measure of disease burden.

Purpose Systemic therapy has improved rhabdomyosarcoma event-free and overall survival; however, approximately 40 % of patients will have progressive or recurrent disease which is difficult to cure and remains a considerable challenge. Minimal progress has been made in improving outcomes for metastatic or relapsed RMS due to a lack of effective therapeutic agents. Targeted therapies are likely to be incorporated into regimens which rely on conventional cytotoxic chemotherapy. A system to evaluate novel combinations of interest is needed. Methods In this study, we explored 8 agents, 5 that are routinely used or similar to agents used in the clinical management of RMS and 3 biologically targeted agents with novel mechanisms of action, the Wee1 inhibitor AZD1775, the tyrosine kinase inhibitor cabozantinib, and the proteasome inhibitor bortezomib. All were tested individually at clinically achievable concentrations for activity in 4 RMS cell lines and then for potential synergy in two-drug combinations. Results We found single-agent activity in five of the agents (or their active metabolites) that constitute the standard of care in RMS and for AZD1775 with mean IC50 values of 207 ng/ml, well below clinically achievable levels. In addition, the combination of individual cytotoxic chemotherapeutics currently used for RMS demonstrated largely synergistic activity with higher, but clinically achievable concentrations of AZD1775 in our assays. Conclusions Prioritization of chemotherapeutics in RMS is possible using an in vitro system that can define novel drug combinations worthy of future investigation. AZD1775 exhibits single-agent activity, as well as synergy with conventional cytotoxic chemotherapy, and is a novel targeted agent that warrants further study in RMS. Electronic supplementary material The online version of this article (doi:10.1007/s00280-016-3077-8) contains supplementary material, which is available to authorized users.

Introduction: HER2 is expressed in a subset of pediatric solid tumors and is a target of interest for innovative immune therapies including CAR-T cells and antibody-drug conjugates (ADCs). We evaluated preclinical efficacy of T-DXd, a humanized monoclonal HER2 antibody conjugated to a topoisomerase 1 inhibitor payload, DXd, in solid tumor patient derived xenograft (PDX) models. Methods: 7 osteosarcoma (OS), 2 rhabdoid tumor (RT) and 3 Wilms tumor (WT) PDX models with varying HER2 expression were tested using 10 mice per group. ERBB2 mRNA expression was determined using RNA seq. T-DXd or vehicle control was administered IV to mice harboring flank tumors at a dose of 5mg/kg on Day 1. Standard PPTC statistical methods were employed for EFS for treatment (T) and control (C) groups, minimum relative tumor volume (minRTV) and objective response measure. Results: Among PPTC solid tumor models ERBB2 mRNA expression was observed across multiple histologies, with highest expression observed for WT (median = 22 FPKM), followed by RT, OS, and Ewing sarcoma. The relationship between HER2 expression by IHC and by RNAseq was inconsistent. Mice tolerated T-DXd with minimal toxicity. T-DXd significantly prolonged EFS in 5/7 OS, 2/2 RT and 3/3 WT PDX models (see table). Complete response (CR) or maintained CR were observed for 4 of 5 WT and RT models, while stable disease was the best response among OS models. Conclusions: T-DXd exhibits single agent anti-tumor activity in models of pediatric solid tumors. Single mouse testing experiments will be used to extend knowledge of the range of activity of T-DXd for pediatric solid tumors. Correlations between ERBB2 gene expression, HER2 expression by IHC, and genetic changes associated with camptothecin sensitivity are ongoing and will be presented. Clinical trials assessing efficacy of a HER2-directed ADC in pediatric patients with HER2-expressing tumors should be considered. EFS T - C(days)EFS T/C Ratiop-value Gehan-WilcoxonminRTVmean±SDminRTVp-valueObjective Response MeasureOS-120.31.85p < 0.0011.152±0.090p = 0.023PD1OS-230.12.76p < 0.0010.815±0.183p < 0.001PD2OS-94.11.14p = 0.1031.334±0.203p = 1.000PD1OS-1734.01.97p = 0.0091.172±0.179p = 0.017PD1OS-3111.91.84p < 0.0011.676±0.395p = 0.015PD1OS-3361.34.87p < 0.0010.486±0.220p < 0.001SDOS-603.81.11p = 0.0161.084±0.103p = 0.007PD1BT29 (RT)> 58.4> 3.28p < 0.0010.019±0.041p < 0.001MCRRBD2 (RT)> 97.3> 13.57p < 0.0010.021±0.066p < 0.001CRKT-10 (WT)> 85.1> 7.57p < 0.0010.000±0.000p < 0.001MCRKT-11 (WT)18.32.62p < 0.0010.954±0.486p < 0.001PD2KT-13 (WT)> 71.5> 3.69p < 0.0010.019±0.060p < 0.001MCR Citation Format: Pooja Hingorani, Wendong Zhang, Raushan Kurmasheva, Zhongting Zhang, Yifei Wang, Zhaohui Xu, Michael Roth, Jonathan Gill, Douglas Harrison, Stephen Erickson, Edward A. Kolb, Malcolm Smith, Peter Houghton, Richard Gorlick. Preclinical evaluation of trastuzumab deruxtecan (T-DXd; DS-8201a), a HER2 antibody-drug conjugate, in pediatric solid tumors by the Pediatric Preclinical Testing Consortium (PPTC) [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 LB-217.

Osteosarcoma (OS) is the most common primary malignant bone tumor in pediatric patients. However, the survival rate of patients with osteosarcomas has not improved for the last several decades. Current developments in immunotherapeutic strategies may increase the efficacy of these treatments for solid tumors. However, these treatments, such as antibody-drug conjugates (ADCs) or CAR-T cell therapy have not been sufficiently studied in OS because of a lack of known tumor-specific target. In this study, we developed an integrative pipeline combining the transcriptomic data from OS patients and the cell-surface proteomics data generated from a panel of patient-derived OS cell lines and PDX models and relating these to normal tissue expression. RNA sequencing data from 40 high-risk OS patients treated at MD Anderson Cancer Center was pooled with 111 OS patients available through the public TARGET online database. All the tumor data was subsequently compared with normal tissue RNA-sequencing data from the NIH Genotype-Tissue Expression (GTEx) database. The significantly differentially expressed genes (log fold change tumor versus normal >1.5 for each tissue, p < 0.01) were selected. We further filtered this gene list by cell surface protein prediction based on the Compartments subcellular localization database. To determine protein expression levels, we prepared surface protein extracts from a panel of patient-derived OS cell lines and PDX models. Proteomic mass spectrometry was used to profile these OS surface proteins. We also included the proteomics data of OS tissue and 39 types of normal human organs via the public proteomic database. Integrative analysis of the transcriptomic and proteomic data demonstrated MMP14, MRC2, and CD276 are highly expressed in OS compared to normal tissues across all datasets. The expression of the three cell surface proteins was validated by IHC staining with an OS tissue microarray from 100 patients, and western blot with our PDX tissues and patient-derived cell lines. A previously reported preclinical study has shown the CD276 ADC (mCD276-PBD) has good antitumor activity against xenograft models of OS. Multiple preclinical tests including CD276 CAR-T cells, MRC2 ADC and MMP14 Bicycle Drug Conjugate (BT1718) are planned to further validate the therapeutic potential of these targets. Our current findings have not been previously reported in OS. The results might warrant further development of ADC and CAR-T cell therapy for osteosarcomas against these targets. Citation Format: Yifei Wang, Zhongting Zhang, Wendong Zhang, Zhaohui Xu, Xin Zhou, Michael Roth, Jonathan Gill, Douglas Harrison, Pooja Hingorani, Sankar Kannan, Sylvester Jusu, Xiangjun Tian, Jing Wang, Rossana Lazcano, Alexander Lazar, Richard Gorlick. Integrative surfaceome profiling identifies MMP14, MRC2 and CD276 as candidate immunotherapeutic target in osteosarcomas [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 5405.

TPS3645 Background: Pre-clinical studies of aerosol gemcitabine (GCB) in mice and dogs with osteosarcoma (OS) lung metastases demonstrated therapeutic efficacy. Aerosol GCB administered once weekly proved to be safe in adults with lung cancer. Direct delivery of GCB to the lungs via inhalation may offer higher drug concentration in the tumor with fewer side effects. We initiated a Phase I study to evaluate the feasibility and safety of aerosol GCB treatment in patients >12 years with solid tumors and lung metastases (2015-0720- NCT03093909). Methods: Eligibility criteria: 1) Diagnosis of solid tumor with lung metastases, 2) willing to comply with protocol therapy, 3) adequate organ function, 4) patient age > 12 and < 50 years, 5) good performance status, 6) resolution of all acute toxic effects of any prior anti-cancer therapy, and 7) no radiotherapy within 2 weeks. Patients who previously received systemic GCB are eligible. Objectives: To determine the maximum tolerated dose (MTD) and toxicities of aerosol GCB, to evaluate for drug spillover into the circulation, and to preliminarily assess the anti-tumor activity. Correlative studies include effect of aerosol GCB on immune cell infiltration in the lung, autophagy, apoptosis, heat shock protein 27, evidence of DNA strand breaks (gH2AX) and expression of human equilibrative nucleoside transporter-1.Aerosol GCB is administered via a breath-induced nebulizer twice a week in 28-day cycles. A maximum of 6 dose levels will be studied; the starting dose is 0.75 mg/kg twice weekly. If no progressive disease or unacceptable treatment-related toxicity, patients may continue for 12 cycles. The study uses the accelerated titration method for the first 2 dose levels then the 3+3 design for the remaining dose levels. After determining the MTD, we will evaluate the defined MTD in an expansion cohort of 14 patients with relapsed OS. Symptoms, pulse oximetry, and pulmonary function are assessed prior to each nebulized dose using remote spirometry that allows raw numbers and flow-volume curves to be uploaded and transmitted via bluetooth to an android tablet provided to patients. Data is transmitted to a web portal and captured in a HIPAA-compliant web-based database (REDCap) that is accessible to the research team. Results: To date, the study enrolled 4 patients and accrual is ongoing at dose level 3. Conclusions: This study will provide information on the feasibility and safety of aerosol GCB. If proven to be feasible and safe, it can potentially offer a novel approach to treat metastatic OS to the lungs while minimizing systemic toxicity. Clinical trial information: NCT03093909 .

TPS11567 Background: Ewing sarcoma (ES) is a rare, aggressive bone and soft tissue cancer that predominantly afflicts adolescents and young adults. Novel therapeutic agents are needed as there are no approved targeted treatments for this disease. ES is characterized by a chromosomal translocation resulting in an EWS/ETS fusion oncoprotein, a transcription factor that results in aberrant gene expression leading to ES progression. Lysine specific demethylase 1 (LSD1) associates with EWS/ETS oncoproteins to alter gene expression and contribute to disease progression. Directly inhibiting EWS/ETS is challenging and little progress has been made, though targeting LSD1 presents a viable therapeutic strategy for ES. Seclidemstat (SP-2577, Salarius Pharmaceuticals) is a first-in-class, orally bioavailable, small molecule with reversible and noncompetitive selective inhibition of LSD1 at low nanomolar concentrations (IC50: 25-50 nM). Seclidemstat inhibits LSD1’s scaffolding functions and enzymatic activity to help reverse aberrant gene expression. In vitro data show that treatment with seclidemstat, or seclidemstat analog, modulates EWS/ETS transcriptional activity, down-regulating oncogene expression and up-regulating tumor-suppressor gene expression. In in vivo xenograft studies (e.g., SK-N-MC, A673), mice treated with seclidemstat show significant tumor growth inhibition/regression vs the control vehicle group. Methods: This phase 1/2 clinical study of seclidemstat is being conducted in relapsed or refractory ES (NCT03600649). The trial is an open-label, non-randomized dose-escalation/dose-expansion study designed to determine the maximum tolerated dose through single-patient dose escalation followed by traditional 3+3 design. The primary objective is to assess seclidemstat’s safety and tolerability while secondary objectives include pharmacokinetics, efficacy and exploratory pharmacodynamic markers. Patients must be ≥12 years old, have received at least 1 prior line of therapy including a prior camptothecin-based regimen, with a life expectancy > 4 months. All patients receive seclidemstat twice-daily (BID) as oral tablets until unacceptable toxicity or disease progression. Patients are followed for survival until the end of study. The trial is currently recruiting across 8 locations in the United States. Upon identification of the recommended phase 2 dose, that cohort will be expanded to enroll a total of 20 patients. Clinical trial information: NCT03600649 .

Pediatric patients with rhabdomyosarcoma (RMS) of the head and neck (HN) are treated with multimodal therapy, often with radiotherapy (RT) as definitive local therapy. We report on the patterns of failure following proton beam therapy (PBT) for HN RMS.Forty-six HN RMS patients were enrolled on a prospective registry protocol between 2006 and 2015. All were treated with a combination of chemotherapy (ChT) and PBT. Most patients (25 patients, 54%) had parameningeal tumors, of which 11 (24%) had intracranial extension (ICE). Thirteen patients (28%) had primary tumors greater than 5 cm. Median total cyclophosphamide (CPM) equivalent dose was 13.2 g/mWith median follow-up of 3.9 years, five-year overall survival was 76%, and five-year progression-free survival was 57%. Seventeen patients (37%) experienced relapse, including 7 with local failure (LF). Five-year local control (LC) was 84%. Tumor size greater than 5 cm predicted increased risk of LF (hazard ratio [HR] 6.49, p = 0.03), as did the presence of ICE at diagnosis (HR 5.21, p = 0.03). Six relapses occurred in patients with ICE; all included a component of central nervous system relapse, with leptomeningeal disease and/or LF with an intracranial component. Delayed RT delivery after week 4 of ChT predicted increased risk of relapse for ICE patients (HR 10.49, p = 0.006).PBT confers excellent LC, and a favorable late toxicity profile as compared with prior photon RT data. Our observations support ongoing trial efforts to dose-escalate RT for patients with larger tumors. However, these data raise concerns regarding excess failures among patients with ICE.

Mixed germ cell tumors (GCT) with teratoma components can transform into somatic malignancies which can include histologies outside of traditional germ cell lineages. We describe a case of an 18-year-old man with a metastatic testicular GCT with both mature and immature teratoma components containing malignant transformation into multiple histologies including PNET in the primary testicular tumor and osteosarcoma in a separate pulmonary metastatic lesion. Management with targeted chemotherapy resulted in a durable remission. This is the first reported case that we know of a patient with primary PNET malignant transformation with subsequent metastatic transformation to osteosarcoma.

Current treatment of osteosarcoma includes surgical resection of all gross disease in conjunction with systemic chemotherapy to control micro-metastatic disease. This yields a 5-year event free survival (EFS) of approximately 70% for patients with localized osteosarcoma while patients with metastatic or recurrent disease fare poorly with overall survival rates of less than 20%. Areas covered: This review outlines the current and future approach towards the treatment of osteosarcoma. A literature search was performed utilizing PubMed. Several recent clinical trials are reviewed in detail, as is innovative research evaluating novel agents and surgical techniques which hold promise. Expert commentary: The outcome for patients with osteosarcoma has not changed in several decades. This plateau in survival rates highlights the need for a novel approach towards research. There remains a great deal of interest in utilizing the very high risk population of recurrent osteosarcoma patients to rapidly and sequentially evaluate novel agents to determine if any of these agents hold promise. Several phase II studies are ongoing or in development that offer hope based on intriguing preclinical data. Furthermore, initiatives in obtaining specimens to further explore the genetic and immunological profile behind osteosarcoma will be essential towards identifying novel pathways and targets to exploit.

Treatment for osteosarcoma, the most common malignant tumor of bone in children and adolescents, has not changed in decades. Treatment is multimodal, employing neoadjuvant chemotherapy followed by aggressive and complete surgical resection to achieve negative margins and a prolonged course of adjuvant chemotherapy. The primary tumor is usually successfully managed via surgery, but micrometastases are likely present in most patients at diagnosis. Death is the result of tumor recurrence in the lungs or more rarely in other bones despite aggressive treatment regimens and is likely attributable to innate resistance to chemotherapy. Better therapies are desperately needed. The three most active agents-high-dose methotrexate, doxorubicin, and cisplatin-commonly referred to as "MAP," form the backbone of therapy. After 2 cycles of MAP, surgical resection is performed of all sites of disease if possible. Histologic response following neoadjuvant chemotherapy is prognostic in non-metastatic osteosarcoma, but augmentation of adjuvant therapy for poor responders with additional agents (ifosfamide, etoposide) has not improved outcome. Inclusion of immunotherapy into treatment regimens is promising. Specifically, liposome-encapsulated muramyl tripeptide phosphatidylethanolamine (L-MTP-PE), a macrophage and monocyte activator, improved 10-year overall survival for patients with localized disease, with a similar pattern of response in patients with metastatic disease. L-MTP-PE (mifamurtide) is approved and in widespread use in Europe and elsewhere but has not been approved for use by the Federal Drug Administration in the USA. Identifying novel targeted therapies to improve outcomes for patients with osteosarcoma remains an area of active research.

10038 Background: Regorafenib is a multi-kinase inhibitor, developed by adding a fluorine atom to the phenyl ring of sorafenib. Regorafenib inhibits multiple kinases including BRAF, FGFR1, KIT, PDGFRB, RAF, RET, and VEGFR1-3, many at a higher potency than sorafenib. Prior studies within the Pediatric Preclinical Testing Consortium (PPTC) demonstrated sorafenib exhibited intermediate activity for tumor growth inhibition in more than 50% of the sarcoma models tested at a dose of 60mg/kg by oral gavage daily (5 days/wk for 6 consecutive weeks). The in vivo effects of regorafenib were studied in the PPTC osteosarcoma (OS), rhabdomyosarcoma (Rh) and Ewing (EW) sarcoma xenograft models. Methods: The in vivo anticancer effects of regorafenib were assessed in a panel of 6 osteosarcoma models (OS2, OS9, OS31, OS33, OS36, OS60), two rhabdomyosarcoma models (Rh30, Rh41), and one Ewing sarcoma model (EW5). Regorafenib was administered by oral gavage at a dose of 30 mg/kg/day given daily for 21 consecutive days. Time to event and tumor volume responses were defined and analyzed utilizing standard PPTC statistical methods. Results: Regorafenib induced significant improvements in event-free survival (EFS) compared to control in 100% (9/9) of sarcoma models tested. Most models showed pronounced slowing of tumor growth compared to control during the 21 days of regorafenib treatment, with tumor growth generally approximating control rates soon after completion of regorafenib treatment. Three out of 8 sarcoma models demonstrated EFS T/C values > 2 (1/6 OS, 2/2 Rh, 0/1 EW). Minimum relative tumor volumes ranged from 0.74 to 1.60, with no models meeting criteria for objective response. Conclusions: Regorafenib induced modest inhibition of tumor growth in the PPTC sarcoma models evaluated. The overall pattern of response to the multi-kinase inhibitor regorafenib against the PPTC sarcoma models appears similar to that of the kinase inhibitor sorafenib, with pronounced slowing of tumor growth in some models that is limited to the period of agent administration being the primary treatment effect.

e21504 Background: Outcomes for patients with metastatic or recurrent sarcomas remains dismal with < 20% overall survival. Due to the rarity of sarcomas, the development, testing, and approval of new therapies takes years. Most early phase clinical trials are restricted to adults leaving young patients with limited options. Little is known about the prevalence and clinical characteristics of patients receiving off-label targeted therapy (OLTT). In this multi-institutional retrospective review we evaluated OLTT use in this population. Methods: Patients with recurrent sarcoma diagnosed between the years of 2008 – 2016 were identified at six institutions. Charts were reviewed for OLTT use and additional clinical characteristics. ANOVA [Analysis of Variance] and Kruskal Wallis Rank sum tests were used for normally and non-normally distributed continuous data. Categorical data was analyzed using chi-squared tests or fisher exact tests. Results: The prevalence of OLTT use was 29% for the patients included in our analysis. Of the 99 cases, the mean age for OLTT was 18 years, ranging 3 – 34 years. Nearly half had recurrent tumor in multiple sites at the time of OLTT use, and 64% did not undergo resection prior to OLTT. Lack of clinical trial availability was the most common reason for OLTT use (31% of cases). The most common OLTT drug class used were tyrosine kinase inhibitors. Progression in 81% of cases was the primary reason for stopping OLTT and toxicity limited use in 12% of cases. One case had a complete response, 5 cases had a partial response and 4 cases had stable disease per RECIST. Conclusions: OLTT use is exceedingly prevalent in patients with recurrent sarcoma. Clinical trials for children and adolescents with recurrent sarcoma will identify optimal agents to improve outcomes in this understudied population.

Background Alveolar soft part sarcoma (ASPS) is a rare mesenchymal tumor characterized by ASPL-TFE3 translocation. Apart from complete surgical resection, there is no standard management strategy. Procedure The clinical data of 69 children and young adults less than 30 years old with ASPS diagnosed from 1980-2014 were retrospectively collected from four major institutions. Results Median age at diagnosis was 17 years (range: 1.5-30). Forty-four (64%) were female. Median follow-up was 46 months (range: 1-409). Most common primary sites were limbs (58%) and trunk (24%). ASPL-TFE3 translocation was present in all 26 patients tested. IRS postsurgical staging was I in 19 (28%), II in 7 (10%), III in 5 (7%), and IV in 38 (55%) patients. The 5-year event-free survival (EFS) and overall survival (OS) were 38% and 72%, respectively. The 5-year EFS and OS were 80% and 87%, respectively, for the 31 patients with localized tumors (IRS-I-II-III), and 7% and 61%, respectively, for the 38 patients with metastatic tumors (IRS-IV). Of 11 IRS-IV patients who received targeted therapy upfront, two had partial response, six had stable disease, and three had progressive disease. Median time to progression for IRS-IV patients was 12 months for those treated with targeted therapy, 7 months for cytotoxic chemotherapy (N = 15), and 4 months for observation only (N = 6). Conclusion Localized ASPS has a good prognosis after gross total resection. ASPS is resistant to cytotoxic chemotherapy. Although there are no curative therapies for patients with metastatic disease, prolonged disease stabilization may be achieved with targeted therapies.

e22019 Background: 30% of male cancer patients receive gonadotoxic therapy that results in infertility. Research exploring male cancer survivors’ attitudes regarding risk of infertility has focused on adults. To understand how AYA survivors perceive their risk of fertility, a cross sectional survey was conducted of male AYA survivors of pediatric cancer. Methods: After IRB approval, the home institution’s database was queried to identify subjects. Eligibility criteria included male survivors between the ages of 15-25 years who had completed treatment in the last 5 years. A self-report survey was designed to assess perspectives of male survivors of pediatric cancer on survivorship with a focus on fertility. Descriptive analysis was performed for all demographic variables collected. To identify whether there was an association between specific demographic variables on survivors’ perspectives regarding their fertility, Fisher’s Exact Test was used (cut-off p-value: 0.05). Results: 33 patients enrolled. Two were deemed ineligible (n = 31). Median age was 20 yrs. Disease and treatment demographics encompassed a wide range of diagnoses and therapy. Subjects were evenly divided as to whether they expected difficulty siring a successful pregnancy. No demographic variable was significantly associated with survivors’ belief that they would have difficulty. A majority recalled being informed during treatment that they may have difficulty siring a pregnancy and having been offered sperm cryopreservation. Of the 22 patients who did not participate in cryopreservation, 12 reported they would have done so to protect their fertility; one would not. Subjects were split as to whether they would have waited to start treatment to allow for cryopreservation. Conclusions: Male survivors of pediatric malignancy are concerned with their future fertility and are informed regarding their risk. Male patients should be counseled regarding their fertility risk and options for fertility preservation. [Table: see text]

We report two infants with infantile fibrosarcoma (IFS) complicated by severe hypercalcemia. Assessment demonstrated suppressed parathyroid hormone and 1,25-dihydroxyvitamin D levels with elevated circulating levels of parathyroid hormone related protein, indicating the diagnosis of humoral hypercalcemia of malignancy (HHM). HHM is a paraneoplastic syndrome rarely associated with pediatric malignancies. Hypercalcemia manifested clinically with neurologic symptoms and soft tissue calcium deposition and required aggressive management with intravenous fluids, diuretics, and supplemental electrolytes. Following treatment with neoadjuvant chemotherapy, serum calcium levels precipitously declined requiring calcium repletion. These cases highlight the improvement of hypercalcemia secondary to HHM following chemotherapy.

10549Background: Change in tumor size by anatomic imaging is not a reliable predictor of outcome in RMS. We reviewed metabolic response by FDG-PET for patients with IR and HR RMS enrolled on two CO...

11069Background: ARMS is considered to be one of the most aggressive pediatric malignancies. Adults with ARMS notoriously experience inferior outcomes. Our goal was to define our adult population w...

This study was performed to determine if a simulated legal deposition increases emergency medicine (EM) residents' knowledge, self-confidence, and understanding of a legal deposition. This prospective study included a convenience sample of EM 1-3 residents. A knowledge and a self-assessment pretest weregiven, followed by a didactic session moderated by local attorneys, followed by knowledge and a self-assessment posttest. The total time involved was 2 hours. The mean score on the knowledge pretest was 4.5 and 5.25 on the posttest. Using a paried t-test, the authors found this difference to be statistically signifi:cant. (P < 0.01) Using HoteUing's T2 test, the authors compared presimulation and postsimulation self-assessment questions. The results r~vealed that there was a difference between these scores (P < 0.001). Participants in the deposition significantly improved their self-assessment ranking and knowledge inventory test scores by participating in a simulated legal deposition.