Treatment practices and response in kaposiform hemangioendothelioma: A multicenter cohort study.

BACKGROUND AND OBJECTIVES: Kaposiform hemangioendothelioma (KHE) and tufted angioma (TA) are rare vascular tumors in children historically associated with significant morbidity and mortality. This study was conducted to determine first-line therapy in the absence of available prospective clinical trials. METHODS: Patients from 17 institutions diagnosed with KHE/TA between 2005 and 2020 with more than 6 months of follow-up were included. Response rates to sirolimus and vincristine were compared at 3 and 6 months. Durability of response and response to other treatment modalities were also evaluated. RESULTS: Of 159 unique KHE/TA subjects, Kasabach-Merritt phenomenon (KMP) was present in 64 (40.3%), and only two patients were deceased (1.3%). Over 60% (n = 96) demonstrated treatment response at 3 months, and more than 70% (n = 114) by 6 months (no significant difference across groups). The vincristine group had higher radiologic response at 3 months compared to sirolimus (72.7% vs. 20%, p = .03), but there were no differences between these groups at 6 months. There were no differences in rates of recurrent or progressive disease between vincristine and sirolimus. CONCLUSIONS: In this large, multicenter cohort of 159 patients with KHE/TA, rates of KMP were consistent with historical literature, but the mortality rate (1.3%) was much lower. Overall treatment response rates were high (>70%), and there was no significant difference in treatment response or durability of disease comparing sirolimus to vincristine. Our results support individualized treatment decision plans depending on clinical scenario and patient/physician preferences. Response criteria and response rates reported here will be useful for guiding future treatment protocols for vascular tumors.

EGFR internal tandem duplications in fusion-negative congenital and neonatal spindle cell tumors.

Next-generation sequencing (NGS) assays can sensitively detect somatic variation, and increasingly can enable the identification of complex structural rearrangements. A subset of infantile spindle cell sarcomas, particularly congenital mesoblastic nephromas with classic or mixed histology, have structural rearrangement in the form of internal tandem duplications (ITD) involving EGFR. We performed prospective analysis to identify EGFR ITD through clinical or research studies, as well as retrospective analysis to quantify the frequency of EGFR ITD in pediatric sarcomas. Within our institution, three tumors with EGFR ITD were prospectively identified, all occurring in patients less than 1 year of age at diagnosis, including two renal tumors and one mediastinal soft tissue tumor. These three cases exhibited both cellular and mixed cellular and classic histology. All patients had no evidence of disease progression off therapy, despite incomplete resection. To extend our analysis and quantify the frequency of EGFR ITD in pediatric sarcomas, we retrospectively analyzed a cohort of tumors (n = 90) that were previously negative for clinical RT-PCR-based fusion testing. We identified EGFR ITD in three analyzed cases, all in patients less than 1 year of age (n = 18; 3/18, 17%). Here we expand the spectrum of tumors with EGFR ITD to congenital soft tissue tumors and report an unusual example of an EGFR ITD in a tumor with cellular congenital mesoblastic nephroma histology. We also highlight the importance of appropriate test selection and bioinformatic analysis for identification of this genomic alteration that is unexpectedly common in congenital and infantile spindle cell tumors.

A comparative analysis of RAS variants in patients with disorders of somatic mosaicism.

PURPOSE: RAS genes (HRAS, KRAS, and NRAS) are commonly found to be mutated in cancers, and activating RAS variants are also found in disorders of somatic mosaicism (DoSM). A survey of the mutational spectrum of RAS variants in DoSM has not been performed. METHODS: A total of 938 individuals with suspected DoSM underwent high-sensitivity clinical next-generation sequencing-based testing. We investigated the mutational spectrum and genotype-phenotype associations of mosaic RAS variants. RESULTS: In this article, we present a series of individuals with DoSM with RAS variants. Classic hotspots, including Gly12, Gly13, and Gln61 constituted the majority of RAS variants observed in DoSM. Furthermore, we present 12 individuals with HRAS and KRAS in-frame duplication/insertion (dup/ins) variants in the switch II domain. Among the 18.3% individuals with RAS in-frame dup/ins variants, clinical findings were mainly associated with vascular malformations. Hotspots were associated with a broad phenotypic spectrum, including vascular tumors, vascular malformations, nevoid proliferations, segmental overgrowth, digital anomalies, and combinations of these. The median age at testing was higher and the variant allelic fraction was lower in individuals with in-frame dup/ins variants than those in individuals with mosaic RAS hotspots. CONCLUSION: Our work provides insight into the allelic and clinical heterogeneity of mosaic RAS variants in nonmalignant conditions.

The genomic landscape of undifferentiated embryonal sarcoma of the liver is typified by C19MC structural rearrangement and overexpression combined with TP53 mutation or loss.

Undifferentiated embryonal sarcoma of the liver (UESL) is a rare and aggressive malignancy. Though the molecular underpinnings of this cancer have been largely unexplored, recurrent chromosomal breakpoints affecting a noncoding region on chr19q13, which includes the chromosome 19 microRNA cluster (C19MC), have been reported in several cases. We performed comprehensive molecular profiling on samples from 14 patients diagnosed with UESL. Congruent with prior reports, we identified structural variants in chr19q13 in 10 of 13 evaluable tumors. From whole transcriptome sequencing, we observed striking expressional activity of the entire C19MC region. Concordantly, in 7 of 7 samples undergoing miRNAseq, we observed hyperexpression of the miRNAs within this cluster to levels >100 fold compared to matched normal tissue or a non-C19MC amplified cancer cell line. Concurrent TP53 mutation or copy number loss was identified in all evaluable tumors with evidence of C19MC overexpression. We find that C19MC miRNAs exhibit significant negative correlation to TP53 regulatory miRNAs and K-Ras regulatory miRNAs. Using RNA-seq we identified that pathways relevant to cellular differentiation as well as mRNA translation machinery are transcriptionally enriched in UESL. In summary, utilizing a combination of next-generation sequencing and high-density arrays we identify the combination of C19MC hyperexpression via chromosomal structural event with TP53 mutation or loss as highly recurrent genomic features of UESL.

How we approach genetics in the diagnosis and management of vascular anomalies.

Vascular anomalies are a heterogeneous group of disorders that are currently classified based on their clinical and histological characteristics. Over the past decade, there have been significant advances in molecular genetics that have led to identification of genetic alterations associated with vascular tumors, vascular malformations, and syndromes. Here, we describe known genetic alterations in vascular anomalies, discuss when and how to test, and examine how identification of causative genetic mutations provides for better management of these disorders through improved understanding of their pathogenesis and increasing use of targeted therapeutic agents in order to achieve better outcomes for our patients.

Chemotherapy-induced thrombocytopenia in Ewing sarcoma: Implications and potential for romiplostim supportive care.

BACKGROUND: Maintaining dose-dense, interval-compressed chemotherapy improves survival in patients with Ewing sarcoma but is limited by myelosuppression. Romiplostim is a thrombopoietin receptor agonist that may be useful in the treatment of chemotherapy-induced thrombocytopenia (CIT). METHODS: Patients aged between 3 and 33 years with Ewing sarcoma from 2010 to 2020 were reviewed. CIT was defined as a failure to achieve 75,000 platelets per microliter by day 21 after the start of any chemotherapy cycle. Fisher's exact test was used for univariate analysis and Pearson's correlation coefficient was used for the association between continuous variables. RESULTS: Twenty-seven out of 42 patients (64%) developed isolated CIT, delaying one to four chemotherapy cycles per patient. CIT occurred during consolidation therapy in 24/27(88.9%) and with ifosfamide/etoposide cycles in 24/27 (88.9%). Univariate analysis failed to identify risk factors for CIT. The use of radiation approached significance (p-value = .056). Ten patients received romiplostim. The median starting dose was 3 µg/kg (range 1-5). Doses were escalated weekly by 1-2 to 4-10 µg/kg and continued throughout chemotherapy. A higher romiplostim dose was associated with a higher change in average platelet counts from baseline, r = .73 (p = .04). No romiplostim-related adverse events were identified aside from mild headache. CONCLUSIONS: CIT is the primary reason for the inability to maintain treatment intensity in Ewing sarcoma. The concurrent use of romiplostim with chemotherapy was safe and feasible, and efficacy was associated with higher romiplostim doses.

Is Detection of Relapse by Surveillance Imaging Associated With Longer Survival in Patients With Rhabdomyosarcoma?

BACKGROUND: We investigated whether surveillance imaging had an impact on post-relapse survival in patients with rhabdomyosarcoma (RMS). We hypothesized that relapse detected by imaging (group IM) would be associated with longer survival compared with relapse detected with a clinical sign or symptom (group SS). MATERIALS AND METHODS: We performed an observational multi-institutional study in 127 patients with relapsed RMS comparing overall survival (OS) after relapse using Kaplan-Meier and Cox proportional hazards analyses. RESULTS: Relapse was detected in 60 (47%) group IM and 67 (53%) SS patients. Median follow-up in survivors was 4 years (range 1.0 to 16.7 y). Four-year OS rates were similar between group IM (28%, 95% confidence interval [CI]: 14%-40%) and SS (21%, 95% CI: 11%-31%) ( P =0.14). In multivariable analyses accounting for institution, age at diagnosis, time to relapse, risk group at diagnosis, and primary site, not receiving chemotherapy (hazard ratio [HR]: 6.8, 95% CI: 2.8-16.6), radiation (HR: 3, 95% CI: 1.7-5.3), or surgery (HR: 2.8, 95% CI: 1.6-4.8) after relapse were independently associated with poor OS. CONCLUSION: These results on whether surveillance imaging provides survival benefit in patients with relapsed RMS are inconclusive. Larger studies are needed to justify current surveillance recommendations. Chemotherapy, radiotherapy and surgery to treat recurrence prolong OS.

Discovery of clinically relevant fusions in pediatric cancer.

BACKGROUND: Pediatric cancers typically have a distinct genomic landscape when compared to adult cancers and frequently carry somatic gene fusion events that alter gene expression and drive tumorigenesis. Sensitive and specific detection of gene fusions through the analysis of next-generation-based RNA sequencing (RNA-Seq) data is computationally challenging and may be confounded by low tumor cellularity or underlying genomic complexity. Furthermore, numerous computational tools are available to identify fusions from supporting RNA-Seq reads, yet each algorithm demonstrates unique variability in sensitivity and precision, and no clearly superior approach currently exists. To overcome these challenges, we have developed an ensemble fusion calling approach to increase the accuracy of identifying fusions. RESULTS: Our Ensemble Fusion (EnFusion) approach utilizes seven fusion calling algorithms: Arriba, CICERO, FusionMap, FusionCatcher, JAFFA, MapSplice, and STAR-Fusion, which are packaged as a fully automated pipeline using Docker and Amazon Web Services (AWS) serverless technology. This method uses paired end RNA-Seq sequence reads as input, and the output from each algorithm is examined to identify fusions detected by a consensus of at least three algorithms. These consensus fusion results are filtered by comparison to an internal database to remove likely artifactual fusions occurring at high frequencies in our internal cohort, while a "known fusion list" prevents failure to report known pathogenic events. We have employed the EnFusion pipeline on RNA-Seq data from 229 patients with pediatric cancer or blood disorders studied under an IRB-approved protocol. The samples consist of 138 central nervous system tumors, 73 solid tumors, and 18 hematologic malignancies or disorders. The combination of an ensemble fusion-calling pipeline and a knowledge-based filtering strategy identified 67 clinically relevant fusions among our cohort (diagnostic yield of 29.3%), including RBPMS-MET, BCAN-NTRK1, and TRIM22-BRAF fusions. Following clinical confirmation and reporting in the patient's medical record, both known and novel fusions provided medically meaningful information. CONCLUSIONS: The EnFusion pipeline offers a streamlined approach to discover fusions in cancer, at higher levels of sensitivity and accuracy than single algorithm methods. Furthermore, this method accurately identifies driver fusions in pediatric cancer, providing clinical impact by contributing evidence to diagnosis and, when appropriate, indicating targeted therapies.

Evaluating Age-related Disparity of Outcomes in Ewing Sarcoma Patients Treated at a Pediatric Academic Medical Center.

Adolescent and young adult (AYA) patients with Ewing sarcoma have inferior survival compared with pediatric patients even when treated with similar regimens. Investigation into specific explanations is lacking. A retrospective chart review of Ewing sarcoma patients at a single institution was performed, and 104 patients were identified, 45 were 15 to 39 years of age (AYA cohort) and 59 younger than 15 years (pediatric cohort). AYA patients demonstrated more metastatic disease (50% vs. 24%, P=0.009), peripheral tumor location (64% vs. 41%, P=0.025), percentage of male patients (76% vs. 51%; P=0.010), and tumor size ≥5 cm (93% vs. 70%, P=0.016) than pediatric patients. Five-year overall survival was 77.7% and 53.0% and event-free survival was 68.7% and 40.6% for pediatric versus AYA, respectively. Similar rates of toxicity and chemotherapeutic dose adjustments were demonstrated. In this cohort, increased AYA patient mortality appears to be related to disease characteristics rather than treatment-related differences.

Bilateral Lung Metastases From a Phalangeal Giant Cell Tumor of Bone.

We describe a rare pediatric case of a phalangeal giant cell tumor of bone with extensive bilateral lung metastases following curettage, wide resection, and amputation. Concurrent peripheral blood eosinophilia and pleural effusion with marked eosinophilia (47%) were present. To discover genetic changes driving tumor metastasis, genomic and transcriptome profiling of the metastatic lung mass as well as germline analysis were performed. Whole exome sequencing detected a histone H3F3A p.G35V missense mutation in tumor cells. RNA sequencing revealed overexpression of receptor activator of nuclear factor kappa-B ligand (RANKL). The patient is alive with no residual disease and uncompromised respiratory function 29 months after amputation of primary tumor and 19 months after surgical resection of his metastatic lung disease.

Phase II trial of gemcitabine and nab-paclitaxel in patients with recurrent Ewing sarcoma: A report from the National Pediatric Cancer Foundation.

BACKGROUND: The combination of gemcitabine and docetaxel is often used to treat patients with recurrent sarcoma. Nab-paclitaxel is a taxane modified to improve drug exposure and increase intratumoral accumulation and, in combination with gemcitabine, is standard therapy for pancreatic cancer. Applying the dosages and schedule used for pancreatic cancer, we performed a phase II trial to assess the response rate of gemcitabine and nab-paclitaxel in patients with relapsed Ewing sarcoma. PROCEDURE: Using a Simon's two-stage design to identify a response rate of ≥ 35%, patients received nab-paclitaxel 125 mg/m2 followed by gemcitabine 1000 mg/m2 i.v. on days 1, 8, and 15 of four-week cycles. Immunohistochemical analysis of archival tissue was performed to identify possible biomarkers of response. RESULTS: Eleven patients from four institutions enrolled, with a median age of 22 years (range, 14-27). Patients were heavily pretreated (median 3 prior regimens, range, 1-7). Thirty-five cycles were administered (median 2, range, 1-8). Accrual was stopped after 11 patients, due to only one confirmed partial response. Two other patients had partial responses after two cycles, but withdrew because of adverse effects or progression before confirmation of continued response. The predominant toxicity was myelosuppression, and four (36%) patients were removed due to hematologic toxicity despite pegfilgrastim and dose reductions. Expression of secreted protein, acidic and rich in cysteine (SPARC) and CAV-1 in archival tumors was not predictive of clinical benefit in this small cohort of patients. CONCLUSIONS: In patients with heavily pretreated Ewing sarcoma, the confirmed response rate of 9% was similar to multi-institutional studies of gemcitabine and docetaxel.

First-in-Human Intravenous Seprehvir in Young Cancer Patients: A Phase 1 Clinical Trial.

Seprehvir (HSV1716) is an oncolytic herpes simplex virus-1 (HSV-1) previously demonstrated to be well tolerated in pediatric patients when administered intratumorally. To determine the safety of administering Seprehvir systemically, we conducted the first-in-human phase I trial of intravenous injection in young patients with relapsed or refractory extra-cranial solid cancers. We delivered a single dose of 5 × 104 infectious units (iu)/kg (maximum dose of 2 × 106) or 2.5 × 105 iu/kg (maximum dose of 1 × 107 iu) of Seprehvir via the peripheral vein, monitored adverse events, and measured tumor responses by imaging. We monitored HSV-1 serology as well as viremia and shedding by PCR and culture. We administered a single dose of Seprehvir to seven patients and multiple doses to two patients. We did not observe any dose-limiting toxicities. All five HSV-1 seronegative patients seroconverted by day 28. Four of nine patients had detectable HSV-1 genomes in peripheral blood appearing on day +4 consistent with de novo virus replication. Two patients had stable disease in response to Seprehvir. Intravenous Seprehvir is well tolerated without viral shedding in children and young adults with late-stage cancer. Viremia consistent with virus replication holds promise for future Seprehvir studies at higher doses and/or in combination with other anti-neoplastic therapies.

Aneursymal Bone Cyst: An Uncommon Paraspinal Tumor in Children.

Paraspinal tumors with benign histology in the absence of trauma rarely arise in children. Treatment of such benign tumors, in contrast to malignancies, generally consists of surgical resection of the lesion with confirmation of histology via pathologic evaluation. We present a pediatric case of an atraumatic paraspinal mass with a histologic diagnosis of aneurysmal bone cyst, and USP6 gene rearrangement supporting the histologic diagnosis. The patient underwent gross total resection of the paraspinal lesion with no additional intervention. We highlight the differential diagnosis of paraspinal tumors in children and key features that led to the diagnosis in this patient.

A Rare Case of an Intracardiac Myoepithelial Carcinoma in an Infant.

Myoepithelial carcinomas (MC) represent aggressive tumors that occur in a myriad of ages and anatomic locations. The rarity and histologic similarity with other tumors make them difficult to diagnosis. We report an extremely rare case of a right ventricular outflow tract mass identified to be an intracardiac MC in a 4-month-old male infant. Pathology revealed an EWS-KLF15 translocation. Treatment included gross total resection and intensive chemotherapy. Recurrent cardiac mass with brain metastasis was seen 16 months after primary diagnosis. We describe the rarity of intracardiac MC in pediatric patients and the challenges encountered in the multimodal management of this patient.

A phase I window, dose escalating and safety trial of metformin in combination with induction chemotherapy in relapsed refractory acute lymphoblastic leukemia: Metformin with induction chemotherapy of vincristine, dexamethasone, PEG-asparaginase, and doxorubicin.

BACKGROUND: Acute lymphoblastic leukemia (ALL) remains a major cause of death in children. AMP-activated protein kinase (AMPK) affects the unfolded protein response (UPR), leading to increased vulnerability to endoplasmic reticulum (ER) stress in ALL cells. In vitro, metformin causes ALL cell death via AMPK-mediated inhibition of the UPR. It was evaluated whether ER stress could be induced in relapsed ALL through a phase I study investigating the safety and feasibility of metformin in combination with relapse induction chemotherapy. PROCEDURE: Metformin was administered twice daily for 28 days in addition to vincristine, dexamethasone, PEG-asparaginase and doxorubicin (VXLD). Dose escalation of metformin was evaluated using a 3+3 design. Pharmacokinetics (PK), pharmacodynamic (PD) evaluation of the AMPK and ER stress/UPR pathways, and treatment response were assessed. RESULTS: Fourteen patients were enrolled; all were evaluable for toxicity. The recommended phase 2 dose (RP2D) was Dose level 2, 1,000 mg/m2 /day. A single dose-limiting toxicity (DLT), hypoglycemia with acidosis, was observed at the RP2D and two DLTs, diarrhea and acidosis, were observed at Dose Level 3. Nine patients were evaluable for response as defined by the protocol, receiving at least 85% of planned metformin doses. Five complete remissions, one partial response, and one stable disease were observed. PD evaluation showed induction of ER stress, activation of AMPK, and inhibition of the UPR. CONCLUSIONS: The VXLD with metformin was tolerable with a RP2D for metformin of 1,000 mg/m2 /day and yielded responses in a heavily pretreated population. ER stress was induced and toxicities attributable to metformin occurred in all dose levels.

VIncristine, irinotecan, and temozolomide in children and adolescents with relapsed rhabdomyosarcoma.

BACKGROUND: The combination of vincristine, irinotecan, and temozolomide (VIT) is often used to treat children and adolescents with relapsed rhabdomyosarcoma (RMS); however, the outcome of these patients has not been previously described. PROCEDURES: We sought to determine the response rate (RR) and progression-free survival (PFS) for patients with relapsed RMS treated with VIT by retrospective review of patients treated at five tertiary care hospitals. Prior treatment with irinotecan was permitted. RESULTS: Among 19 patients with a median age of 8 years (range 2-17 years), 12 (63%) were males and 12 (63%) had embryonal histology. Median time to relapse from initial diagnosis was 16 months (range 2.8-45 months). VIT was used as first, second, third, or fourth line of therapy in four (21%), seven (37%), six (32%), and two (10%) patients, respectively. Four patients received VIT as adjuvant therapy following radiation and/or surgery. Therefore, among 15 evaluable patients, the best response to VIT was 0 (complete response, CR), 0 (partial response, PR), 4 (stable disease, SD), and 11 (progressive disease, PD) for an overall clinical benefit rate (CR + PR + SD) of 26.7% (95% CI: 7.8-55.1%). After a median follow-up of 8 months, 2 (10%) patients were alive without disease, 3 (16%) were alive with disease, and 14 (74%) patients died of PD. PFS at 3 months was 23% (95% CI: 5.7-46.7%). CONCLUSIONS: VIT therapy in combination with adequate local control is associated with some disease control in patients with first relapse RMS and may be another reasonable option to offer patients as salvage therapy.

Romiplostim for therapy-related thrombocytopenia in pediatric malignancies.

Therapy-related thrombocytopenia (TRT), due to chemotherapy and/or radiation therapy, is common with pediatric cancer treatments, and it can result in dose reductions and therapy delays. Romiplostim, a thrombopoietin mimetic, is efficacious as a second-line treatment for immune thrombocytopenia in children and for TRT in adult cancer patients. However, there are no data for its use for TRT in children. We report a case series of five children treated for solid tumors where romiplostim was used without adverse effects to successfully resolve and prevent therapy-limiting refractory TRT. Prospective studies on this use of romiplostim are warranted.

Rhabdomyosarcoma of the Breast in Adolescent and Young Adult (AYA) Women.

Soft tissue sarcoma constitutes 8% of all tumors in adolescent and young adults (AYA), with rhabdomyosarcoma (RMS) accounting for 5.2% to 6.5% of the soft tissue sarcoma total within this group. AYAs have a higher propensity for metastasis and inferior outcomes. Metastases to the breast have been reported in ∼3% to 6% of RMS cases. A review of our hospital's tumor registry identified cases of RMS diagnosed between January 1, 2004 and December 31, 2013. A total of 46 patients with RMS were identified, having a mean age of 12.5 years (range, 1 to 49 y). There were 26 males (57%) and 20 females (43%). Eighteen patients (39%) were AYAs, including 10 women. Four patients (8.7%) were identified with breast involvement, all of whom were AYA females. Treatment modalities included chemotherapy, surgical resection, and radiation. One patient is a long-term survivor. Although RMS is uncommon in AYAs, breast involvement occurs almost exclusively in AYA women and is associated with alveolar histology, metastatic disease, and poor outcomes. In total, 4/10 of all AYA females had breast involvement. Routine examination or imaging of the breasts in AYAs with RMS is not currently standard practice at diagnosis or follow-up, but this analysis suggests it should be considered in female AYA patients.

Hypoxic Proliferation of Osteosarcoma Cells Depends on Arginase II.

BACKGROUND/AIMS: Despite significant advancements in the diagnosis and treatment of osteosarcoma, the overall survival has remained relatively unchanged for over two decades. Hypoxic conditions have been demonstrated in solid tumors and are associated with increased cell proliferation and angiogenesis. L-arginine metabolism by arginase produces L-ornithine, the precursor for polyamine and proline synthesis required for cellular proliferation. We hypothesized that hypoxia would increase cellular proliferation via arginase induction in human osteosarcoma cell lines. METHODS: We utilized a variety of approaches to examine the role of arginase II in hypoxic (1% O2, 5% CO2) cellular proliferation. RESULTS: Arginase II mRNA and protein levels were significantly increased in osteosarcoma cells exposed to hypoxia for 48 hours. There were twice as many viable cells following 48 hours of hypoxia than following 48 hours of normoxia (21% O2, 5% CO2). The addition of difluoromethylornithine (DFMO), a putative arginase inhibitor, prevented hypoxia-induced proliferation. Transfection of small interfering RNAs (siRNA) targeting arginase II resulted in knockdown of arginase II protein levels and prevented hypoxia-induced cellular proliferation. CONCLUSIONS: These data support our hypothesis that hypoxia increases proliferation of osteosarcoma cells in an arginase II-dependent manner. We speculate that arginase II may represent a therapeutic target in osteosarcoma.

Disease Control and Toxicity Outcomes after Stereotactic Ablative Radiation Therapy for Recurrent and/or Metastatic Cancers in Young-Adult and Pediatric Patients.

BACKGROUND: Pediatric patients with metastatic and/or recurrent solid tumors have poor survival outcomes despite standard-of-care systemic therapy. Stereotactic ablative radiation therapy (SABR) may improve tumor control. We report the outcomes with the use of SABR in our pediatric solid tumor population. METHODS: This was a single-institutional study in patients < 30 years treated with SABR. The primary endpoint was local control (LC), while the secondary endpoints were progression-free survival (PFS), overall survival (OS), and toxicity. The survival analysis was performed using Kaplan-Meier estimates in R v4.2.3. RESULTS: In total, 48 patients receiving 135 SABR courses were included. The median age was 15.6 years (interquartile range, IQR 14-23 y) and the median follow-up was 18.1 months (IQR: 7.7-29.1). The median SABR dose was 30 Gy (IQR 25-35 Gy). The most common primary histologies were Ewing sarcoma (25%), rhabdomyosarcoma (17%), osteosarcoma (13%), and central nervous system (CNS) gliomas (13%). Furthermore, 57% of patients had oligometastatic disease (≤5 lesions) at the time of SABR. The one-year LC, PFS, and OS rates were 94%, 22%, and 70%, respectively. No grade 4 or higher toxicities were observed, while the rates of any grade 1, 2, and 3 toxicities were 11.8%, 3.7%, and 4.4%, respectively. Patients with oligometastatic disease, lung, or brain metastases and those who underwent surgery for a metastatic site had a significantly longer PFS. LC at 1-year was significantly higher for patients with a sarcoma histology (95.7% vs. 86.5%, p = 0.01) and for those who received a biological equivalent dose (BED10) > 48 Gy (100% vs. 91.2%, p = 0.001). CONCLUSIONS: SABR is well tolerated in pediatric patients with 1-year local failure and OS rates of <10% and 70%, respectively. Future studies evaluating SABR in combination with systemic therapy are needed to address progression outside of the irradiated field.