Mhlanga, Joyce

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.

Abstract Background National Cancer Institute-Children’s Oncology Group Pediatric Molecular Analysis for Therapy Choice assigns patients aged 1-21 years with refractory solid tumors, brain tumors, lymphomas, and histiocytic disorders to phase II trials of molecularly targeted therapies based on detection of predefined genetic alterations. Patients whose tumors harbored EZH2 mutations or loss of SMARCB1 or SMARCA4 by immunohistochemistry were treated with EZH2 inhibitor tazemetostat. Methods Patients received tazemetostat for 28-day cycles until disease progression or intolerable toxicity (max 26 cycles). The primary endpoint was objective response rate; secondary endpoints included progression-free survival and tolerability of tazemetostat. Results Twenty patients (median age = 5 years) enrolled, all evaluable for response and toxicities. The most frequent diagnoses were atypical teratoid rhabdoid tumor (n = 8) and malignant rhabdoid tumor (n = 4). Actionable alterations consisted of SMARCB1 loss (n = 16), EZH2 mutation (n = 3), and SMARCA4 loss (n = 1). One objective response was observed in a patient with non-Langerhans cell histiocytosis with SMARCA4 loss (26 cycles, 1200 mg/m2/dose twice daily). Four patients with SMARCB1 loss had a best response of stable disease: epithelioid sarcoma (n = 2), atypical teratoid rhabdoid tumor (n = 1), and renal medullary carcinoma (n = 1). Six-month progression-free survival was 35% (95% confidence interval [CI] = 15.7% to 55.2%) and 6-month overall survival was 45% (95% CI = 23.1% to 64.7%). Treatment-related adverse events were consistent with prior tazemetostat reports. Conclusions Although tazemetostat did not meet its primary efficacy endpoint in this population of refractory pediatric tumors (objective response rate = 5%, 90% CI = 1% to 20%), 25% of patients with multiple histologic diagnoses experienced prolonged stable disease of 6 months and over (range = 9-26 cycles), suggesting a potential effect of tazemetostat on disease stabilization.

AbstractImaging in hematopoietic stem cell transplantation patients is not targeted at evaluating the transplant per se. Rather, imaging is largely confined to evaluating peri‐procedural and post‐procedural complications. Alternatively, imaging may be performed to establish a baseline study for comparison should the patient develop certain post‐procedural complications. This article looks to describe the various imaging modalities available with recommendations for which imaging study should be performed in specific complications. We also provide select imaging protocols for different indications and modalities for the purpose of establishing a set minimal standard for imaging in these complex patients.

10009 Background: The NCI-Children’s Oncology Group (COG) Pediatric Molecular Analysis for Therapy Choice (MATCH) trial assigns patients, age 1-21 years, with relapsed or refractory solid tumors, lymphomas, and histiocytic disorders to phase 2 treatment arms based on genetic alterations detected in their tumor. Arm C evaluated the EZH2 inhibitor tazemetostat in patients whose tumors harbored EZH2 hotspot mutations or SMARCB1 or SMARCA4 loss by immunohistochemistry. Methods: Tazemetostat 1200 mg/m2/dose PO BID was administered to the first 13 patients; after study amendment due to second malignancy noted in the pediatric phase 1 trial, the dose for patients with non-CNS tumors was reduced to 520 mg/m2/dose PO BID. Patients were treated for 28-day cycles until PD or intolerable toxicity (max 26 cycles); response assessments occurred every 2-3 cycles. Primary and secondary endpoints were ORR and PFS, respectively. Results: Twenty eligible and evaluable patients (median age 5 years; range 1-21) were enrolled between Nov 2017 and Sept 2020. SMARCB1 loss was detected in 16/20 (80%) tumors: atypical teratoid rhabdoid tumor (ATRT, n = 8), malignant rhabdoid tumor (MRT, n = 4), epithelioid sarcoma (ES, n = 2), renal medullary carcinoma (RMC, n = 1) and hepatocellular carcinoma (HCC, n = 1). EZH2 mutations were identified in 3/20 (15%) tumors: Ewing sarcoma (n = 2), ependymoma (n = 1). One patient with Langerhans cell histiocytosis (LCH) had SMARCA4 loss. Centrally reviewed, one objective response (PR) was observed (LCH [SMARCA4], 26 cycles at 1200 mg/m2/dose BID). Five other patients had a best response of stable disease (ES [SMARCB1], 26 cycles, 520 mg/m2/dose BID; ATRT [SMARCB1], 13 cycles,1200 mg/m2/dose BID; RMC [SMARCB1], 12 cycles, 520 mg/m2/dose BID; ES [SMARCB1], 9 cycles,1200 mg/m2/dose BID; ATRT [SMARCB1], 6 cycles, 1200 mg/m2/dose BID). No other patients received > 2 cycles. Six-month PFS was 35% (95% CI 15.7%, 55.2%); OS was 45% (95% CI 23.1%, 64.7%). Treatment-related adverse events were consistent with AEs previously reported with tazemetostat, including anemia, thrombocytopenia, elevated LFTs, abdominal pain, dyspnea, infection, and intracranial hemorrhage. Three patients had bromide elevations. Conclusions: In this cohort of children with relapsed tumors harboring EZH2 mutations or loss of SMARCB1 or SMARCA4, tazemetostat did not produce significant objective responses (ORR: 5%, 90% CI 1%, 20%). However, we observed prolonged stable disease of > 6 months (range: 6-26 cycles) in 33% of patients across different histologic diagnoses, including two patients who received the full two years of study therapysuggesting a potential effect of tazemetostat on disease stabilization. Future studies will incorporate tazemetostat in combination with chemotherapy or immunologic agents for patients with these aggressive and difficult to treat tumors. Clinical trial information: NCT03213665.

PURPOSE The NCI-COG Pediatric MATCH trial assigns patients age 1-21 years with relapsed or refractory solid tumors, lymphomas, and histiocytic disorders to phase II studies of molecularly targeted therapies on the basis of detection of predefined genetic alterations. Patients with tumors harboring mutations or fusions driving activation of the mitogen-activated protein kinase (MAPK) pathway were treated with the MEK inhibitor selumetinib. METHODS Patients received selumetinib twice daily for 28-day cycles until disease progression or intolerable toxicity. The primary end point was objective response rate; secondary end points included progression-free survival and tolerability of selumetinib. RESULTS Twenty patients (median age: 14 years) were treated. All were evaluable for response and toxicities. The most frequent diagnoses were high-grade glioma (HGG; n = 7) and rhabdomyosarcoma (n = 7). Twenty-one actionable mutations were detected: hotspot mutations in KRAS (n = 8), NRAS (n = 3), and HRAS (n = 1), inactivating mutations in NF1 (n = 7), and BRAF V600E (n = 2). No objective responses were observed. Three patients had a best response of stable disease including two patients with HGG ( NF1 mutation, six cycles; KRAS mutation, 12 cycles). Six-month progression-free survival was 15% (95% CI, 4 to 34). Five patients (25%) experienced a grade 3 or higher adverse event that was possibly or probably attributable to study drug. CONCLUSION A national histology-agnostic molecular screening strategy was effective at identifying children and young adults eligible for treatment with selumetinib in the first Pediatric MATCH treatment arm to be completed. MEK inhibitors have demonstrated promising responses in some pediatric tumors (eg, low-grade glioma and plexiform neurofibroma). However, selumetinib in this cohort with treatment-refractory tumors harboring MAPK alterations demonstrated limited efficacy, indicating that pathway mutation status alone is insufficient to predict response to selumetinib monotherapy for pediatric cancers.

10509 Background: PST allows for improved surgical outcomes and response assessment without compromising long term outcomes. PST is an attractive model for assessing surrogate markers of response to therapy. We hypothesized that changes in tumor standardized uptake values corrected for lean body mass (SUL) max on FDG- PET by cycle 1 day 15 (C1D15) of therapy would predict pathological complete response (pCR) to PST in women with stage 2-3, grade 2-3, HER2-negative breast cancer. Methods: TBCRC008 is a multicenter placebo-controlled trial that investigates pCR following 12 weeks of preoperative carboplatin and albumin-bound paclitaxel with or without vorinostat. FDG-PET followed by tumor biopsies were performed at baseline and C1D15. We correlated % reduction in SULmax on FDG-PET (PERCIST 1.0; Wahl RL, J Nuc Med 2009) with pCR (no invasive cancer in breast/axilla). We compared % reduction in SULmax between responders (pCR) and non responders (no pCR) using nonparametric Wilcoxon rank sum test. We explored association of % reduction in SULmax at pre-specified cutoff with response using Fisher’s exact test and logistic regression. We correlated baseline, C1D15, and % change in Ki67 at C1D15 with pCR. Results: Accrual is complete. Of 62 women enrolled (10/2009-11/2011), 40 have completed study PST and surgery (median age 47.5 [range 30-68], ER-positive 67%). Overall pCR was 26%. In an intent to treat analysis (n=39), we observed a significant difference in median % reduction in SULmax between responders vs not (66.6% vs 32.4%, p <0.001). We observed a higher proportion of reduction in SULmax ≥ 60% in responders vs not (80% vs 3.5%, p <0.001). The differences in baseline, C1D15 and % change in Ki67 were not significant between responders and non-responders. Conclusions: Change in SULmax on FDG-PET 15 days after initiating PST was significantly greater in patients with pCR versus no pCR. Future studies will determine whether altering therapy based on early changes in SULmax will improve pCR. Unblinded data from all participants will be presented at the meeting.