A Comparison of Clinical Outcomes for Subependymal Giant Cell Astrocytomas Treated with Laser Interstitial Thermal Therapy, Open Surgical Resection, and mTOR Inhibitors

INTRODUCTION

Subependymal giant cell astrocytoma (SEGA) is the most common CNS tumor in patients with tuberous sclerosis complex (TSC). Although these are benign, their proximity to the foramen of Monroe frequently causes obstructive hydrocephalus, a potentially fatal complication. Open surgical resection has been the mainstay of treatment; however, this can cause significant morbidity. The development of mTOR inhibitors has changed the treatment landscape, but there are limitations to their use. Laser interstitial thermal therapy (LITT) is an emerging treatment modality that has shown promise in treatment of a variety of intracranial lesions, including SEGAs. We present a single institution, retrospective study of patients treated for SEGAs with LITT, open resection, mTOR inhibitors, or a combination of these modalities. The primary study outcome was tumor volume at most recent follow-up compared with volume at treatment initiation. The secondary outcome was clinical complications associated with treatment modality.

METHODS

Retrospective chart review was performed to identify patients with SEGAs treated at our institution from 2010 to 2021. Demographics, treatment information, and complications were collected from the medical record. Tumor volumes were calculated from imaging obtained at initiation of treatment and at most recent follow-up. Kruskal-Wallis nonparametric testing was used to assess differences in tumor volume and follow-up duration between groups.

RESULTS

Four patients underwent LITT (3 with LITT only), three underwent open surgical resection, and four were treated with mTOR inhibitors only. Mean percent tumor volume reduction for each group was 48.6 ± 13.8, 90.7 ± 39.8, and 67.1 ± 17.2%, respectively. No statistically significant difference was identified comparing percent tumor volume reduction between the three groups (p = 0.0513). Additionally, there was no statistically significant difference in follow-up duration between groups (p = 0.223). Only 1 patient in our series required permanent CSF diversion and 4 discontinued or decreased the dose of mTOR inhibitor due to either cost or side effects.

CONCLUSIONS

Our study suggests that LITT could be considered as a treatment option for SEGAs as it was effective in reducing tumor volume with very few complications. This modality is less invasive than open resection and may be an alternative for patients who are not candidates for mTOR inhibitors. We recommend an updated paradigm for SEGA treatment which includes LITT in select cases after consideration of patient-specific factors.

IMMU-09. Interim analysis from BrainChild-03: Seattle Children’s Locoregional B7-H3 CAR T Cell Trial for Children with Recurrent Central Nervous System Tumors and DIPG

BrainChild-03 is a phase 1 clinical trial delivering repeated locoregional 2nd generation B7-H3 CAR T cells with 4-1BB co-stimulation to children with central nervous system (CNS) tumors without lymphodepleting chemotherapy. The primary endpoints are feasibility and safety, with secondary endpoints of disease response and correlatives of CAR T cell activity. There are 3 arms: (A) – weekly delivery into the tumor cavity, (B) – weekly delivery into the lateral ventricle for metastatic disease, (C) – biweekly delivery into the lateral ventricle for diffuse intrinsic pontine glioma (DIPG). In total, 23/24 (96%) enrolled patients have had successful CAR T manufacturing. 16/24 patients are evaluable and have received a total of 141 intracranial CAR T cell doses. Unevaluable patients include 5 never treated and 3 who progressed prior to receiving the minimum doses to become evaluable. The most common adverse events have been headache (16/16, 100%), nausea/vomiting (12/16, 75%), and fever (10/16, 63%). There has been 1 DLT for an intratumoral hemorrhage and no cytokine release syndrome (CRS). 7 evaluable patients with DIPG (Arm C) have received a cumulative 50 infusions. 5/7 DIPG patients enrolled after progression and have a median survival of 246.5 days post-initial CAR T cell infusion, with 4/5 still alive. The 2 DIPG patients enrolled prior to progression had radiographic improvement, including 1 with improvement of a cranial nerve 6 palsy who self-withdrew from protocol therapy after 18 infusions over 12 months and 1 still on protocol therapy after 11 infusions over 6 months. DIPG patients have had increased CSF levels of proinflammatory mediators (e.g. CXCL10, CCL2, IFNg, GM-CSF, IL-12) without systemic cytokine changes. 5/7 DIPG patients had detectable CAR T cells in their CSF post-infusion. Ultimately, the preliminary experience suggests locoregional delivery of B7-H3 CAR T cells may be feasible and tolerable in children with CNS tumors, including DIPG.

OTHR-26. A pilot study of clinical minimal residual disease detection in pediatric embryonal brain tumors

Cell-free DNA (cfDNA) presents an opportunity for measurement of minimal residual disease (MRD) in pediatric central nervous system (CNS) tumors. In this pilot study, we sought to evaluate the clinical use of low-pass whole genome sequencing (LP-WGS) of cfDNA in cerebrospinal fluid (CSF) of patients with embryonal neoplasms. 31 CSF samples were collected from 16 patients with molecularly characterized medulloblastoma (12), embryonal tumor with multilayer rosettes (2), and CNS embryonal tumors, NEC (2). Samples were collected at various treatment time points. Processing included centrifugation and freezing prior to cfDNA extraction, repair, adapter ligation, amplification, purification, and sequencing on an internally-developed and clinically-validated LP-WGS assay utilizing custom-developed bioinformatics and molecular pathologist review. 29 of 31 samples (94%) had adequate cfDNA in CSF for LP-WGS analysis. Copy number variants (CNVs) compatible with tumor were detected in 23 of 29 (79%) samples, including isodicentric chromosome 17, monosomy 6, MYCN amplification, and regional amplification of chromosome 19. In all cases with detectable cfDNA alterations in CSF, CNV were compatible with the molecular findings in tumor tissue. Two CSF samples had additional chromosomal alterations detected at the time of tumor progression that were not identified in the original tumors. All 9 lumbar puncture samples (100%) collected at initial staging had CSF cfDNA alterations indicative of MRD while corresponding cytologic evaluations of the same samples were positive in only 1 of 9 (11%). No MRD was detected in the single sample evaluated at the end of therapy time point. These findings suggest that LP-WGS of cfDNA in CSF represents a sensitive and clinically useful test for detection of MRD in patients with embryonal tumors of the CNS independent from CSF cytology. Future prospective studies are warranted to determine whether LP-WGS analysis of cfDNA in CSF can predict tumor recurrence and early treatment resistance in our patients.

MODL-28. IMMUNE PRIMING WITH INTERFERON-Γ COMBINED WITH EPIGENETIC MODULATION IN PEDIATRIC BRAIN TUMORS

Systemic interferon-γ (IFNγ) has been shown to induce major histocompatibility complex class I (MHC-I) and T cell infiltration in solid tumors in adult patients, demonstrating a potential strategy to abrogate tumor-intrinsic mechanisms of immune escape. Pediatric brain tumors (PBT) may be particularly sensitive to this approach but have a paucity of immunogenic tumor antigens for presentation on MHC-I. Decitabine and other DNA methyltransferase (DNMT) inhibitors promote expression of oncofetal antigens and endogenous immune responses through epigenetic alterations. We tested the convergence of these immune priming mechanisms using a novel combination of IFNγ and decitabine across a spectrum of PBT. Primary human cell lines (Med-411FH, PBT-05FH, GBM-511FH, CCHMC-GBM-1, CCHMC-GBM-4, ATRT-310FH) and murine transgenic models were treated with IFNγ alone or in combination with decitabine and evaluated expression of cell surface MHC-I and PD-L1, interferon response genes (ISGs), and oncofetal antigens. PBT showed exquisite sensitivity to IFNγ, increasing expression of MHC-1/PD-L1 along with ISGs (TAP1, MX1, IRF1). Decitabine enhanced IFNγ-induced gene expression of oncofetal antigens NY-ESO-1 and MAGE-A1. In a medulloblastoma flank tumor model, MHC-I was increased by 40-fold following intraperitoneal IFNγ treatment (p=0.01), with a 3-fold increase in PD-L1 (p=0.005) compared to untreated controls. Effect on CD8+ T cell killing and validation in humanized models is ongoing. Immune priming of PBT with IFNγ is feasible and results in more substantial MHC-I upregulation compared to hypomethylating agents alone. These results provide a strong rationale for priming prior to checkpoint inhibition as a compelling therapeutic strategy in immunologically-quiescent PBT.

TMIC-48. MACROPHAGE DEPLETION COMBINED WITH RADIATION IN A PRECLINICAL MEDULLOBLASTOMA MODEL

BACKGROUND

Radiation induces a measurable immune response, yet this anti-tumor immunity is often suboptimal at eliminating residual brain tumor cells. Medulloblastomas, along with other pediatric brain tumors, tend to recur in the primary resection bed following irradiation. Infiltrating macrophage within the tumor (TAM) are radioresistant immune cells that may limit the effectiveness of radiotherapy and promote tumor regrowth through their immunosuppressive and pro-tumorigenic functions. Therefore, we explored whether CSF-1 receptor (CSF1R) inhibition, and essentially TAM depletion, could augment radiation and/or reduce local recurrence.

METHODS

Selected CSF1R inhibitors were tested on both human and mouse macrophage in vitro. In vivo studies were performed on a patient-derived orthotopic xenograft (PDOX) model of Group 3 medulloblastoma, Med411-FH. Macrophage depletion was achieved using the anti-murine CSF1R antibody, AFS98, injected intra-peritoneally 10 days prior to, concurrently, and after radiation.

RESULTS

CSF1R antibodies and small molecule tyrosine kinase inhibitors were effective at stanching macrophage survival in culture. In a PDOX medulloblastoma model, both classes of CSF1R inhibitors were effective at reducing macrophage in the brain after approximately 10 days of administration, with maximal effect of 90% depletion achieved after 21 days. In a combinatorial study of AFS98 and irradiation, TAM depletion conferred a very modest effect on tumor growth (p=0.003) and had no effect on overall survival when combined with radiation (p=0.86). Interestingly, we did observe a trend toward reduction in metastatic spinal disease following radiation in the AFS98-treated cohort.

CONCLUSION

CSF1R antibody administration effectively eliminated macrophage and microglia in the brain and spine, suggesting adequate blood-brain barrier penetration in our xenograft model. While CSF1R inhibition combined with radiation was ineffective at prolonging survival, further studies are needed to investigate a modest effect on brain tumor growth and an observed (yet not statistically significant) difference in metastatic spinal recurrence in drug-treated animals.

FDG-PET imaging in patients with paraneoplastic syndromes and suspected small cell lung cancer

Paraneoplastic syndromes may be the presenting clinical manifestation of small cell lung cancer. In some cases, however, confirming the diagnosis can be difficult because findings on conventional imaging studies can be subtle or nonspecific. This study examined the utility of fluoro-2-deoxy-glucose positron emission tomography (FDG-PET) in identifying clinically suspected small cell lung cancer in patients with paraneoplastic syndromes. FDG-PET appears to be very useful in localizing suspected small cell lung cancer in patients presenting with paraneoplastic syndromes.

Susceptibility of penicillin-sensitive and -resistant strains of Streptococcus pneumoniae to new antimicrobial agents, including daptomycin, teicoplanin, cefpodoxime and quinolones

The minimal inhibitory concentrations (MICs) of nine antibiotics were determined by agar dilution on 123 strains of Streptococcus pneumoniae (65 penicillin sensitive, 42 intermediate resistant and 16 resistant). The antimicrobial agents tested were penicillin G, clindamycin, trospectomycin, daptomycin, teicoplanin, cefpodoxime, ciprofloxacin, ofloxacin and vancomycin. Of these, daptomycin, teicoplanin and vancomycin demonstrated the greatest in-vitro activity against penicillin-resistant strains (MIC90s less than or equal to 0.25 mg/l). Ciprofloxacin, ofloxacin and trospectomycin had equivalent activities unaffected by penicillin-susceptibility (MIC90 of both quinolones 2.0 mg/l, and of trospectomycin 4.0 mg/l). Cefpodoxime was also active in vitro against all strains (MIC90 2.0 mg/l), but MICs increased with increasing penicillin-MICs. Most penicillin-susceptible strains were susceptible to clindamycin, but many penicillin intermediate resistant and resistant strains were resistant to this drug. Results of this study indicate that several newly introduced and experimental antibiotics have potential in the treatment of infections caused by resistant strains of Str. pneumoniae.