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.