Proton therapy for re-irradiation of pediatric diffuse brain stem tumors

Currently, there is no cure for pediatric diffuse brain stem (BS) tumors. Radiotherapy, including proton therapy, is an important component of combination treatment for this cancer, especially in children with a complicated medical history. The article addresses the issues of therapy for pediatric BS tumors and reports the use of proton re-irradiation in a 9-year-old boy with unverified diffuse BS tumor. Proton re-irradiation is an effective treatment option that can sustain and improve the quality of life and prolong survival in children with diffuse BS tumors.

ITVT-07. Robotic alignment module Cirq for navigated brainstem tumor biopsies

BACKGROUND With the incorporation of the robotic alignment module Cirq (Brainlab, Germany) into our neurosurgical armamentarium, we aimed to know our baseline accuracy in stererotactic biopsies. We therefore retrospectively reviewed our data on biopsy accuracy for brain(stem) tumors using the non-robotic alignment instrument Varioguide (Brainlab, Germany). Because of unexpectedly large deviations from the intended target, we sought to improve our registration accuracy when we introduced Cirq. Intraoperative 3D CT with bone fiducials was added to the pre-operative 3D T1 MRI with skin fiducials. This made it possible to compare surgical devices as well as registration methods. AIMS To share our experience with the new robotic alignment module Cirq for navigated brain(stem) tumor biopsies and to evaluate its target accuracy with bone fiducial registration, as compared to the previously used Varioguide with skin fiducial registration. METHODS All patients (0–18 years old) that underwent a brain(stem) biopsy in our institution were included. Over 2018–2020, data were collected retrospectively (cohort Varioguide with 3D T1 MRI registration with skin fiducials). From 2021, data were collected prospectively (cohort Cirq with both 3D T1 MRI registration with skin fiducials and intraoperative CT registration with bone fiducials). For both cohorts, Euclidian distances were calculated between the intended target and the obtained target. For the prospective cohort, registration errors were calculated for bone versus skin fiducials. PRELIMINARY REUSLTS The deviation from the intended target was much smaller in the Cirq cohort versus the Varioguide cohort. Within the Cirq cohort, registration errors were submillimetric for bone fiducial registration as compared to several millimeters for skin fiducial registration. CONCLUSION: The Cirq robotic arm is convenient, safe and highly accurate, especially when combined with intraoperative 3D CT bone fiducial registration. Skin fiducial registration does not offer the level of precision that is mandatory in brainstem tumor biopsies.

RESULTS OF COMBINED AND INTEGRATED TREATMENT OF BRAIN STEM TUMORS IN ADULTS

Objectives: Analysis results of combined and integrated treatment of brain stem gliomas tumors in adults. Materials and methods: Retrospective analysis was carried out on the basis of clinical material collected from 2010 to 2019 in the radiotherapy clinic of FSBU «RNCRR» of the Ministry of Health of the Russian Federation (RNCRR). A total of 43 people were included in the study. 18 (41.86%) patients underwent surgery or stereotactic biopsy in the first stage of treatment. In the future, all patients underwent remote radiotherapy and/or chemotherapy. According to the results of histologic verification of operated patients, brain gliomas were diagnosed in 100% of cases, with 10 people (23%) showing low grade gliomas (Grade I-II) and 8 (18.6%) showing high grade (Grade III-IV). Evaluation of treatment effectiveness, analysis of general and free survival cumulative disease by Kaplan-Mayer method using IBM SPSS Statistics software. Results: According to the study, the rate of free survival was 48.73 months, and the average general survival time was 51.54 months. Histologic type tumor did not significantly affect the rate of free survival (P. = 0.417), and the results of general survival were significantly higher in the group of patients with low grade gliomas compared to the group of patients with high grade tumors (P. = 0.036). Conclusion: Significant clinical factors must be taken into account when planning the treatment of brain stem tumors.

Malignant Progression of an MDS-Derived Cell Line Serves As an in Vitro Model for the Leukemic Evolution of MDS

Myelodysplastic syndromes (MDS) have a risk of progression to acute myeloid leukemia (AML), but the deterioration mechanisms of MDS and the alteration points still remain to be elucidated. We previously established a myelodysplastic cell line, MDS92 from the bone marrow of an MDS patient, and after a long-term interleukin(IL)-3-containing culture of MDS92, five blastic sublines including MDS-L were isolated. From MDS-L, we obtained two sublines, MDS-L-2007 and MDS-LGF after culture in the presence and absence of IL-3, respectively. To investigate the mechanism of leukemic evolution, we applied a next-generation sequencing (NGS) to the series of cell lines for comprehensive, comparative exome analyses, and searched for the origin of mutations by ultra-deep target sequencing of the original patient bone marrow. Whole exome sequencing and ultra-deep target sequencing demonstrated: (1) TP53 mutation was found in the patient bone marrow and this mutation was inherited by all subsequent cell lines; (2) CEBPA mutation was originally present in a small fraction of the bone marrow; (3) NRAS mutation emerged by chance during IL-3-containing culture; (4) HIST1H3C(K27M) mutation (Histone-H3-K27M) was newly detected at the generation of MDS-L from MDS92. H3-K27M mutation was detected in MDS-L-2007 but not in MDS-LGF. We focused on H3-K27M mutation because it is frequently found in pediatric brain stem tumors and recently found in a small population of AML cases (Lehnertz et al. Blood. 2017). MDS-L cells were a mixture of H3-K27M-mutant and wild-type clones. When MDS-L was cultured in the presence of IL-3, the proportion of H3-K27M-mutant fraction gradually increased. In contrast, when MDS-L was cultured without IL-3, the proportion of H3-K27M-mutant fraction gradually decreased. To investigate the implication of H3-K27M mutation, we tried single cell cloning from MDS-L and secured four wild-type clones and seven H3-K27M-mutant clones. In all H3-K27M-mutant clones, there was a marked reduction in H3-K27me3/2. Expression of a tumor-suppressor molecule p16 was reduced in six of the seven H3-K27M-mutant clones. H3-K27M-mutant clones showed rapid growth in the presence of IL-3, but cell proliferation was suppressed without IL-3. Competitive growth experiment by co-culture of H3-K27-wild-type and H3-K27M-mutant clones in the presence or absence of IL-3 showed that H3-K27M-mutant clones were predominant in the presence of IL-3, whereas wild-type clones were sustained comparatively in the absence of IL-3. Treatment with EPZ-6438, an inhibitor of H3-K27 methyltransferase EZH2, caused growth suppression of H3-K27M-mutant clones as well as wild-type clones and involved obvious recovery of p16 expression in H3-K27M-mutant clones, which provides a possibility that p16 might be a therapeutic target for H3-K27M mutant. Although GSK-J4, an inhibitor of H3-K27 demethylase JMJD3, was reported to inhibit H3-K27M-mutated pediatric brain stem tumors, GSK-J4 exerted only non-specific growth inhibitory effect on both H3-K27M-mutant and wild-type clones. Whole exome analyses indicated that the accumulation of oncogenic mutations seemed to have led to establishment of MDS cell lines. The finding that growth advantage of H3-K27M mutant was influenced by the presence or absence of IL-3 raised a possibility that even if neoplastic clones emerge, their expansion might be influenced not only by genetic/epigenetic status but by surrounding environmental factors including cytokines. This series of cell lines will be a useful tool as an in vitro model for leukemic evolution of MDS. Disclosures No relevant conflicts of interest to declare.