Fox, Elizabeth

PURPOSE Human epidermal growth factor receptor 2 (HER2), a transmembrane receptor with kinase activity involved in cell signaling through the RAS pathway, is expressed in osteosarcoma (OST). Trastuzumab deruxtecan (T-DXd) is an antibody-drug conjugate with a HER2-targeting monoclonal antibody, trastuzumab, linked to a topoisomerase I inhibitor. We report results of a phase II study of T-DXd in adolescents and young adults with HER2-positive relapsed, unresectable OST (ClinicalTrials.gov identifier: NCT04616560 ). METHODS Patients age 12-39 years with relapsed, unresectable OST were eligible for centrally evaluated HER2 expression screening by immunohistochemistry. Patients with >10% of OST cells with cytoplasmic or membranous HER2 expression of any intensity were eligible to receive T-DXd at 5.4 mg/kg intravenously once every 3 weeks for up to 2 years. The study used a 9 + 15 Simon's optimal two-stage design with a primary end point of event-free survival at 24 weeks. RESULTS Fifty patients were screened for HER2, and 41 met the inclusion criteria of 10% of OST cells having membranous or cytoplasmic HER2 expression. Nine eligible patients, two younger than 18 years, were enrolled and received T-DXd. With a single patient having more than 24 weeks of stable disease (SD) of the nine planned in the first stage, this study did not meet criteria to progress to stage II. The estimated SD rate at 24 weeks is 11.1%. The median (range) number of cycles of therapy was 2 (2-12). Grade 3 and 4 possibly related adverse events occurred in three of nine patients and included nausea, vomiting, tumor hemorrhage, cytopenias (n = 3), wound infection, and hypertension. CONCLUSION T-DXd did not demonstrate sufficient activity to expand enrollment to the planned second stage in patients with OST. No new safety signals were observed.

10051 Background: CBL0137 is a novel agent that targets the FAcilitates Chromatin Transcription complex (FACT), a histone chaperone that regulates chromatin remodeling during transcription, replication, and DNA repair. CBL0137 has been shown to have anti-tumor activity in multiple preclinical models of pediatric cancer. We report the phase 1 trial of CBL0137 in children with relapsed or refractory solid tumors including central nervous system (CNS) tumors or lymphoma (NCT04870944). Methods: Patients (age 12 months to 21 years) with relapsed/refractory solid tumors, central nervous system tumors or lymphoma were eligible. In the dose escalation phase, a rolling-six design was used to evaluate CBL0137 administered intravenously (IV) once per week on Days 1 and 8 of a 21-day cycle. The starting dose was 400 mg/m 2 , with escalation to the adult phase 2 dose (RP2D) of 540 mg/m 2 . The maximum tolerated dose (MTD) was determined based on cycle 1 dose limiting toxicity (DLT) using Common Toxicity Criteria for Adverse Events (v5). Pharmacokinetics (PK) and cytokine analyses were performed during cycle 1. Seven additional patients ( < 18 years old) were accrued to a PK expansion cohort at the RP2D. Results: Sixteen patients were enrolled; 14 were evaluable for DLT assessment (12 at 400mg/m 2 [6 in dose escalation and 6 in PK expansion] and 2 at 540mg/m 2 ). The median (range) age was 10 (4-20) years. Diagnoses included high grade glioma (n = 6), osteosarcoma (n = 5), ependymoma (n = 2), neuroblastoma, hepatoblastoma and Burkitt’s lymphoma (1 each). One of 12 evaluable patients treated at 400 mg/m 2 experienced a DLT: Grade 3 photosensitivity. At 540 mg/m 2 , the two evaluable patients both had fever and dose limiting Grade 3 hypotension. Non-dose limiting Grade 3-4 toxicities included anemia, lymphopenia, neutropenia, thrombocytopenia, hypokalemia, anorexia, photosensitivity and fever. For both dose levels, a total of 12 patients were reported to have at least one episode of Grades 1-3 fever and/or Grade 1 cytokine release syndrome (CRS). PK parameters (mean±SD) for CBL0137 (400 mg/m 2 ) were T max = 0.7 ± 0.5 h, C max = 1310 ± 417 ng/mL, and AUC 0-24h = 15300 ± 6790 h·ng/mL. Given the unexpected toxicities of fever, hypotension, and CRS, cytokine samples were collected in patients enrolled in the PK expansion cohort; all had Grade 1 CRS and significantly elevated levels of both IL-10 (adj p = 0.001) and IL-1RA (adj p < 0.001) at 24 hours vs pre-infusion. Conclusions: The RP2D and MTD of CBL0137 in children and adolescents with solid or CNS tumors is 400mg/m 2 IV weekly on Days 1 and 8 of 21-day cycles. CBL0137 leads to immune activation, with cytokine elevation and the possibility of CRS, an unexpected toxicity not previously reported in adults. A Phase 2 cohort in patients with Diffuse Midline Glioma is ongoing and includes further assessment of immune activation. Clinical trial information: NCT04870944 .

TPS2695 Background: The SMARCB1/A4 gene products are core subunits of the SWItch/Sucrose Non Fermentable (SWI/SNF) chromatin remodeling complex. Tumors with defects in SWI/SNF are histologically distinct aggressive cancers occurring in children and young adults. SMARCB1/A4 deficient tumors, particularly malignant rhabdoid tumor (MRT), atypical teratoid rhabdoid tumor (ATRT), poorly differentiated chordoma (PDC), epithelioid sarcoma (ES), and renal medullary carcinoma (RMC), have immune cell infiltrates and programmed death ligand 1 (PD-L1) expression. Responses to immune checkpoint inhibition (CI) have been observed in SMARCB1/A4 deficient tumors; however, responses are not durable. T cell immunoreceptor with Ig and ITIM domains (TIGIT) is a novel inhibitory receptor expressed on multiple immune cells. TIGIT inhibits T and NK cells by binding to its ligand poliovirus receptor (PVR) and Nectin2 on both tumor and antigen-presenting cells. Utilizing RNAseq data, SMARCB1/A4 deficient tumors demonstrate high expression of PVR and Nectin2. Tiragolumab is an antibody to the TIGIT receptor. The combination of tiragolumab and atezolizumab has shown promising activity in early phase studies, and phase 3 studies are ongoing in multiple adult indications. Thus, there is rationale that the addition of tiragolumab to CI may also enhance response rates in patients with SMARCB1/A4 deficient tumors. Methods: This is a phase 1/2 trial of tiragolumab monotherapy (300 mg if ≤ 15 kg; 420 mg if > 15 kg to ≤ 40 kg; 600 mg if > 40 kg or ≥ 18 years) and in combination with atezolizumab (15 mg/kg [max 1200 mg]) if < 18 yrs or 1200 mg if ≥ 18 years) administered IV on Day 1 of 21-day cycles in patients > 12 months of age with SMARCB1/A4 deficient tumors. Part A evaluating the safety of tiragolumab monotherapy in patients < 18 years based on cycle 1 dose limiting toxicities is complete. Part B estimates the antitumor activity of tiragolumab in combination with atezolizumab in 6 histology-specific cohorts (RMC, MRT, ATRT, PDC, ES, and other SMARCB1/A4 deficient tumors) and is now open to all eligible age groups. Each cohort is conducted using a 6+4 Simon’s two stage design. Enrollment for each cohort is as follows: Part A 6/6, Part B RMC 1/6, MRT 1/6, ATRT 4/6, PDC 2/6, ES 3/6, other 6/6. Radiographic imaging central response assessment for the first stage of the “other” cohort is ongoing. Cycle 1 toxicities of the combination therapy are monitored in Part B patients < 12 yrs using a Bayesian Optimal INterval (BOIN) design with a target toxicity of 17%. Secondary objectives are to characterize the pharmacokinetics/anti-drug antibody development and to estimate progression free survival, overall survival, and duration of response. Enrollment is open at all Pediatric Early Phase Clinical Trial Network sites. Data cutoff: Jan 10, 2025. Clinical trial information: NCT05286801 .

Abstract Purpose: Selinexor is a first-in-class, central nervous system (CNS)–penetrant, oral inhibitor of exportin 1 (XPO1), the main nuclear exporter of many key tumor suppressors. We report a phase I trial of selinexor in children and adolescents with recurrent CNS and solid tumors (NCT02323880). Patients and Methods: A rolling six design was used to evaluate the maximum tolerated dose (MTD) and first dose pharmacokinetics of selinexor administered once (35–45 mg/m2) or twice (20–35 mg/m2) weekly during a 28-day cycle (part A). Ten additional patients with high-grade glioma (HGG) were treated at the MTD administered once weekly (part B). Results: In part A, 49 patients were enrolled. Continuous twice weekly dosing was limited by extended hematologic toxicity. The MTD on a twice weekly schedule for 3 weeks on/1 week off (twice weekly 3/1) was 20 mg/m2/dose. Dose-limiting toxicities (DLTs) on this schedule included fatigue, acute reversible neurologic changes, neutropenia, thrombocytopenia, and aspartate aminotransferase/alanine aminotransferase increase. On a continuous once weekly schedule, the MTD was 35 mg/m2/dose; DLTs included seizure and thrombocytopenia. In part B (HGG expansion), there were no additional DLTs observed. Non-DLTs included lymphopenia, leukopenia, neutropenia, thrombocytopenia, anorexia, fatigue, hypophosphatemia, nausea, and vomiting. There were no objective responses. The median number of cycles received was 1 (range, 1–9); eight of 59 patients (13.5%) received 5 to 9 cycles, five of whom had HGG. Conclusions: Selinexor-related toxicities were primarily hematologic and neurologic, requiring dose or dose-frequency reduction. The MTD and recommended initial phase II dose of selinexor in children and adolescents with recurrent solid and CNS tumors is 35 mg/m2/dose once weekly.

PURPOSE The TRK inhibitor larotrectinib is US Food and Drug Administration approved for NTRK fusion–positive solid tumors that lack a satisfactory alternative or have progressed after treatment but has not been systematically studied as a frontline therapy with a defined duration of treatment. ADVL1823 evaluated larotrectinib in patients with newly diagnosed NTRK fusion–positive solid tumors with response-adapted duration of therapy and local control. METHODS Patients received larotrectinib twice daily in 28-day cycles for a predefined duration of treatment, ranging from 6 to 26 cycles depending on response to therapy and surgical resectability. The primary end point was the objective response rate (ORR) within six cycles in patients with infantile fibrosarcoma (IFS); patients with other histologic diagnoses were analyzed in a separate cohort. Secondary objectives included event-free survival (EFS) and overall survival (OS). RESULTS Thirty-three patients were enrolled: 18 with IFS and 15 with other solid tumors. The ORR within six cycles was 94% (17/18; 95% adjusted CI, 72.7 to 98.6) among children with IFS and 60% (9/15; 95% CI, 32.3 to 83.7) among children with other solid tumors. Six percent (2/33; 95% CI, 0.7 to 22.2) patients developed progressive disease while on therapy. Two-year EFS and OS among these groups were 82.2% (95% CI, 54.3 to 93.9) and 93.8% (95% CI, 63.2 to 99.1) for IFS and 80% (95% CI, 50.0 to 93.1) and 93.3% (95% CI, 61.3 to 99.0) for other solid tumors, respectively. Patients undergoing surgical resection of their tumor had prolonged EFS, with only 1 of 16 such patients experiencing disease progression. Four of 33 patients had dose-limiting toxicities. CONCLUSION Larotrectinib is highly active in patients with newly diagnosed NTRK fusion–positive solid tumors. Larotrectinib should be a frontline option for patients with IFS and other NTRK fusion–positive solid tumors. Local control with surgical resection remains important in the treatment of patients with IFS.

ABSTRACT Background Nab ‐sirolimus (ABI‐009, nab ‐rapamycin; Aadi Bioscience Inc. [Aadi]) is a human albumin‐bound form of sirolimus nanoparticles, a potent mTOR inhibitor. This phase I trial was conducted to define dose‐limiting toxicities (DLT), maximum tolerated or recommended phase II dose (MTD/RP2D), and pharmacokinetics of Nab ‐sirolimus in combination with temozolomide and irinotecan. Methods Using a rolling 6 design, Nab ‐sirolimus was administered intravenously (IV) on days (D) 1 and 8 of cycle (C) 1. In subsequent cycles, Nab ‐sirolimus was administered D1 and D8 in combination with temozolomide (125 mg/m 2 /dose, maximum 250 mg/dose) and irinotecan (90 mg/m 2 /dose) orally, daily on D1–5. Cycle duration was 21 days. Three dose levels (DL) of Nab ‐sirolimus were investigated (DL1: 35 mg/m 2 /dose, DL‐1: 20 mg/m 2 /dose, and DL‐2: 15 mg/m 2 /dose). The observation period for estimating the MTD/RP2D was defined by cycles 1 and 2. Results Thirty‐three patients were enrolled, 32 were eligible. Dose determination included 17 evaluable patients, median (range) age 12 (2–20) years and six additional patients were enrolled (four evaluable for toxicity) on a pharmacokinetic cohort. C1 or C2 DLTs were primarily thrombocytopenia including 2/5 patients at DL1, 2/6 patients at DL‐1, and 1/6 patients at DL‐2. One patient (DL1) with Ewing Sarcoma had a partial response and remained on study for 35 cycles. Rapamycin clearance was dose dependent. Irinotecan clearance and its active metabolite SN‐38 exposure were not affected by coadministration with Nab ‐sirolimus. Conclusion The MTD for Nab ‐sirolimus was 15 mg/m 2 /dose IV on D1 and D8 in combination with temozolomide 125 mg/m 2 /dose and oral irinotecan 90 mg/m 2 /dose daily for 5 days during 21D cycles. Trial Registration ClinicalTrials.gov identifier NCT02975882

PURPOSE The National Cancer Institute-Children's Oncology Group Pediatric Molecular Analysis for Therapy Choice trial assigned patients age 1-21 years with relapsed or refractory solid tumors, lymphomas, and histiocytic disorders to phase II treatment arms of molecularly targeted therapies on the basis of genetic alterations detected in their tumor. Patients with tumors that harbored prespecified genomic alterations in the cyclinD-CDK4/6-INK4a-Rb pathway with intact Rb expression were assigned and treated with the cdk4/6 inhibitor palbociclib. METHODS Patients received palbociclib orally once daily for 21 days of 28-day cycles until disease progression, intolerable toxicity, or up to 2 years. The primary end point was objective response rate; secondary end points included safety/tolerability and progression-free survival. RESULTS Twenty-three patients (median age, 15 years; range, 8-21) were enrolled; 20 received protocol therapy and were evaluable for toxicity and response. Of the evaluable patients, the most common diagnoses were osteosarcoma (n = 9) and rhabdomyosarcoma (n = 6). A single actionable gene amplification was found in 19 tumors ( CDK4 , n = 11, CDK6 , n = 2, CCND3 , n = 6), with one tumor harboring two amplifications ( CDK4 and CCND2 ). Hematologic toxicities were the most common treatment-related events. No objective responses were seen. Two patients with tumors harboring CDK4 amplifications (neuroblastoma and sarcoma) had best response of stable disease for six and three cycles. Six-month progression was 10% (95% CI, 1.7 to 27.2). CONCLUSION The CDK4/6 inhibitor palbociclib at 75 mg/m 2 orally daily was tolerable in this heavily pretreated cohort. No objective responses were observed in this histology-agnostic biomarker-selected population with treatment-refractory solid tumors, demonstrating that pathway alteration alone is insufficient in pediatric cancers to generate a response to palbociclib monotherapy.

PURPOSE Patients age 1-21 years with relapsed or refractory solid and CNS tumors were assigned to phase II studies of molecularly targeted therapies on the National Cancer Institute-Children's Oncology Group (NCI-COG) Pediatric Molecular Analysis for Therapy Choice (MATCH) trial. Patients whose tumors harbored predefined genetic alterations in the phosphoinositide 3-kinase (PI3K)/mammalian target of rapamycin (mTOR) pathway and lacked mitogen-activated protein kinase pathway activating alterations were treated with the PI3K/mTOR inhibitor samotolisib. METHODS Patients received samotolisib twice daily in 28-day cycles until disease progression or unacceptable toxicity. A rolling 6 limited dose escalation was performed as, to our knowledge, this was the first pediatric study of samotolisib. The primary end point was the objective response rate; secondary end points included progression-free survival (PFS) and the recommended phase II dose and toxicity of samotolisib in children. RESULTS A total of 3.4% (41/1,206) of centrally tested patients were matched to this arm. Seventeen patients were treated. Among treated patients, the most common diagnoses included osteosarcoma (n = 6) and high-grade glioma (n = 5) harboring alterations in phosphatase and tensin homolog (n = 6), PIK3CA (n = 5), and tuberous sclerosis complex 2 (n = 3). No objective responses or prolonged stable disease were observed. Three-month PFS was 12% (95% CI, 2 to 31). Two patients experienced dose-limiting toxicities (mucositis and pneumonitis). Dose level 2 (115 mg/m 2 /dose twice daily) was determined to be the recommended phase II dose of samotolisib in children. CONCLUSION This nationwide study was successful at identifying patients and evaluating the efficacy of molecularly targeted therapy for rare molecular subgroups of patients in a histology-agnostic fashion. Unfortunately, there was no activity of samotolisib against tumors with PI3K/mTOR pathway alterations. Prospective trials such as the NCI-COG Pediatric MATCH are necessary to evaluate the efficacy of molecularly targeted therapies given their increasing use in clinical practice.

PURPOSE The National Cancer Institute-Children's Oncology Group (NCI-COG) Pediatric MATCH trial assigns patients age 1-21 years with refractory malignancies to phase II treatment arms of molecularly targeted therapies on the basis of genetic alterations detected in their tumor. Patients with activating alterations in the mitogen-activated protein kinase pathway were treated with ulixertinib, an extracellular signal-regulated kinase (ERK)1/2 inhibitor. METHODS As there were no previous pediatric data, ulixertinib was initially tested in a dose escalation cohort to establish the recommended phase II dose (RP2D) before proceeding to the phase II cohort. Ulixertinib was administered at 260 mg/m2/dose orally twice a day (dose level 1 [DL1], n = 15) or 350 mg/m2/dose orally twice a day (DL2, n = 5). The primary end point was objective response rate; secondary end points included safety/tolerability and progression-free survival (PFS). RESULTS Twenty patients (median 12 years; range, 5-20) were treated, all evaluable for response. CNS tumors comprised 55% (11/20) of diagnoses, with high-grade glioma and low-grade glioma most common (n = 5 each). All CNS tumors except one harbored BRAF fusions or V600E mutations. Rhabdomyosarcoma (n = 5) was the most frequent non-CNS diagnosis. DL1 was declared the RP2D in the dose escalation cohort after dose-limiting toxicities in Cycle 1 occurred in 1/6 patients at DL1 and 2/5 patients at DL2, including fatigue, anorexia, rash, nausea, vomiting, diarrhea, dehydration, hypoalbuminemia, and hypernatremia. No objective responses were observed. Six-month PFS was 37% (95% CI, 17 to 58). Three patients with BRAF-altered CNS tumors achieved stable disease >6 months. CONCLUSION Ulixertinib, a novel targeted agent with no previous pediatric data, was successfully evaluated in a national precision medicine basket trial. The pediatric RP2D of ulixertinib is 260 mg/m2/dose orally twice a day. Limited single-agent efficacy was observed in a biomarker-selected cohort of refractory pediatric tumors.

10015 Background: The Children’s Oncology Group developed and implemented a unified method of dosing anticancer drugs in infants and small children with a BSA < 0.6 m2. The dosing tables use BSA-based dose banding and account for deliverable doses/volumes of the drugs. We studied the PK of VCR (1.5 mg/m2 dose level) in infants and children to determine whether this new infant dosing method achieves uniform drug exposures across the pediatric age span. Methods: We designed a sampling strategy to limit the blood volume required by focusing on the elimination (β) phase of the VCR concentration-time curve, which accounts for > 80% of the total area-under the curve (AUC). Duplicate samples to detect contamination were drawn at 3 post-infusion time points (2, 6-8 and 18-24 hr) through a central venous catheter (CVC) after a 90 min flush. VCR concentrations were measured at the Children’s Hospital of Philadelphia using a validated high-pressure liquid chromatography/tandem mass spectrometry method with a lower limit of quantitation (LLQ) of 0.25 ng/mL. A one-compartment model was fit to the concentration-time data using population PK methods (Phoenix NLME). The AUCβ was derived from the dose and clearance for each patient. Patients were accrued in 4 age groups (≤6 mo, goal n = 20); > 6 mo to ≤12 mo, goal n = 10; > 12 mo to ≤36 mo, goal n = 10; and > 36 mo to ≤12 yr, goal n = 10) to focus on infants and ensure representation across the pediatric age range. Results: 52 eligible patients have been enrolled and 39 are evaluable for PK analysis, including 9 ≤6 mo, 8 > 6 mo and ≤12 mo, 12 > 12 mo and ≤36 mo, and 10 > 36 mo and ≤12 y,. The median (range) age is 13.5 mo (1.15-112 mo). VCR was quantifiable in all samples, and there was no evidence of contamination in the duplicate samples drawn through the CVC. The mean ± SD AUCβ in the 39 evaluable patients was 54.7 ± 19.8 ng⋅h/mL. As shown in the Table, the AUCβ is similar in patients with a BSA < 0.6 m2 dosed according to the BSA-banded infant dosing table and patients with a BSA ≥0.6 m2 dosed by multiplying their BSA times 1.5 mg/m2 (p = 0.53, Mann Whitney test). Conclusions: The VCR BSA-banded infant dosing table appears to provide uniform VCR exposure for infants and young children compared to conventional BSA-based dosing in older children. The study design and sampling strategy facilitated rapid accrual of a young population and generated more VCR PK data in infants within a year than has been published since the drug was approved in 1963. This study demonstrates the feasibility of systematically studying other anticancer drugs in infants and other special populations to ensure they are receiving safe and effective doses. VCR AUCβ by dosing method. Clinical trial information: NCT05359237 . [Table: see text]