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e14027 Background: The existing modern standards of combination treatment of HGG patients do not provide recovery and a long-term favorable prognosis, and the increasong incidence of HGG determines the need for additional effective technologies for anticancer and decongestant therapy. One of such methods involves TMS, and we have reported its preliminary assessment earlier (DOI: 10.1200/JCO.2020.38.15_suppl.2545). In this study, we continued the observation to examine the survival of patients. Methods: Patients with HGG received combination treatment: stage 1 – surgical removal of tumors within visible unaltered tissues; stage 2 – radiation therapy (the Varian Novalis linear accelerator) to the bed of the removed tumor, single boost dose 2 Gy, total boost dose 60 Gy; stage 3 – multi-course chemotherapy: temozolomide 150 mg/m² on days 1-5 with a 23-day interval. Starting from the second day after surgery, patients of group 1 (n = 25) received 10 TMS sessions, and during radiotherapy – 15 TMS sessions. Patients of group 2 (n = 25) received combination treatment without TMS. 6 and 12 months after the surgery, survival of patients was assessed with the Kaplan-Meier method and the Log-Rank test. Results: After 6 months of the follow-up, the survival of patients in group 1 remained at 100%, while in the control group it decreased to 88.8±8.7%. The difference in the 1-year overall survival was even more pronounced: in group 1, it was 68.5±10.4%, exceeding the value in group 2 (52.0±7.5%.) The differences were statistically significant (Log-Rank test p = 0.001). Conclusions: The results confirm the effectiveness of accompanying TMS in the early postoperative period, as well as at the stage of radiation therapy. The undoubted effectiveness of the considered techniques makes it expedient to include this type of treatment in the combination therapy for HGG patients. The reported study was funded by RFBR, project number № 19-315-90082\19.

e14025 Background: The effectiveness of radiation therapy in the classical and stereotactic treatment regimens of the primary glioblastoma multiforme was analyzed and compared. Methods: 87 patients with primary glioblastoma multiforme were hospitalized during the study period. 17 patients of them were in the treatment group (stereotactic radiotherapy, dose per fraction 2 Gy, 60 Gy total dose, CTV 2.0 cm, PTV 0.1 cm - group 1), and 70 patients were in the control group (conventionally fractionated radiotherapy, dose per fraction 2 Gy, 60 Gy total dose, CTV 2.0 cm, PTV 0.5 cm - group 2). Patients of both groups were treated with alkylating agents as the third stage of complex treatment. MGMT methylation was evaluated by pyrosequencing. Results: The use of stereotactic radiation therapy allowed to conduct a full course of treatment without interruption, whereas in the second group, due to the development of adverse reactions, the course was interrupted for 7 patients (10%). The advantage of stereotactic radiation therapy was a less pronounced increase and rapid regression of neurological deficits during treatment, manifested by better local control for 6 months. Hypermethylation of MGMT was detected in 39% of glioblastoma cases and was not detected in non-tumor tissue. The presence of promoter methylation disrupts DNA repair and is associated with longer survival in glioblastoma patients receiving alkylating agents. Note that the median survival of patients with MGMT hypermethylation in the group 1 was 285 days (IQR = 323.75), and in the group without hypermethylation was significantly more than 338.5 days (IQR = 476) (p = 0.045). A similar trend was observed in the second group: in patients with hypermethylated MGMT, the median survival was 271 days (IQR = 337), the result is different from patients without hypermethylated MGMT – 342 days (IQR = 493) (p = 0.039). Conclusions: As a result, the application of the stereotactic approach of radiation therapy in the complex treatment of patients with glioblastoma and their classification by the MGMT methylation status with a cut-off point of 10% has the basis for improving the effectiveness and tolerability of radiation therapy and contributes to the overall survival of patients.

e15011 Background: Poor clinical effects of standard treatment for glioblastoma determine the need for the development of new therapeutic strategies. Aberrant functioning of the proteasome system, as well as activation of the HIF-1α signaling pathway, are characteristic of glial tumor cells; they can be considered as potential therapeutic targets in the treatment of malignant brain tumors. One of the possible options for improving the results of glioblastoma treatment may involve strategies for inhibiting the HIF-1α pathway. Bortezomib, a proteasome inhibitor, can block the biological effects of HIF-1α. Bortezomib showed a pronounced antitumor effect in in vitro testing on various models of solid malignant tumors, giving grounds for further studies of its effectiveness in vivo. Patient-derived xenograft (PDX) models are characterized by a variety of cell subclones and are therefore considered the most reliable tool for predicting therapeutic responses. Methods: A PDX model of glioblastoma was created in 20 Balb/c Nude mice implanted with a subcutaneously inoculated human glioblastoma. Temozolomide (0.5 mg/kg), bortezomib (0.25 mg/kg), or a combination of temozolomide and bortezomib were administered intraperitoneally daily for 21 days. The tumor histotype was confirmed by histological analysis (staining with hematoxylin and eosin). The antitumor effect was determined by the inhibition of tumor growth (ITG%), the volume of tumor nodes, and the index of tumor growth. Results: The highest value of the inhibition of tumor growth (ITG%) was registered in the group of animals receiving a combination of temozolomide and bortezomib – 85.38%. The values in the groups receiving temozolomide or bortezomib monotherapy were 57.32% and 63.11%, respectively. Conclusions: An analysis of the antitumor efficacy of bortezomib combined with temozolomide in human subcutaneous PDX-glioblastomas demonstrated their synergistic effect.

e14000 Background: The purpose of the study was to analyze changes in the total activity of trypsin-like proteinases (TLPs) in the blood plasma in patients with brain tumors for the preoperative differential diagnosis of benign, primary and secondary malignant brain tumors. Methods: TLPs were measured in 164 patients with brain tumors. The blood had been collected from the patients in a standard plastic tube with 3.8% sodium citrate (9:1) 3 days prior to the surgery. Citrate blood was centrifuged; citrated plasma was obtained and used to determine the total TLP activity by the unified kinetic method. Results were compared with the data in donors. Results: TLP activity in 37 (22.6%) of 164 patients was within the normal range (258–402 IU/mL, on the average 333.0±27.1 IU/mL). Benign brain tumors (meningioma) were diagnosed in all 37 patients after the tumor removal and histological analysis. In 74 (45.1%) of 164 patients, TLP activity was within 1158–1626 IU/mL (on the average 1331.0±102.4 IU/mL, p < 0.05), i.e. 3.8-5.3 times higher than the norm in donors (malignancy coefficient on average 4.4±0.3 times). Primary malignant brain tumors (glioblastoma) were diagnosed in all 74 patients after the tumor removal and histological analysis. In 53 (32.3%) of 164 patients, TLP activity was within 1794–2868 IU/mL (on the average 2227.0±174.1 IU/mL, p < 0.05), i.e. 5.9-9.4 times higher than the norm in donors (malignancy coefficient on average 7.3±0.5 times). Secondary malignant brain tumors (metastases) were diagnosed in all 53 patients after the tumor removal and histological analysis. Conclusions: The specificity of the proposed method for the differential diagnosis of brain tumors was very high: for benign tumors - 97.2%, for primary malignant tumors - 98.6% and for secondary malignant tumors - 98.1%. So, TLP activity indices in the blood plasma are an informative auxiliary laboratory test that will help in clarifying and/or confirming the differential diagnosis of brain tumors.