P17.02.B APPLICATION OF METHOTREXATE IN THE TREATMENT OF HIGH-RISK PEDIATRIC MEDULLOBLASTOMA: A RETROSPECTIVE STUDY FROM AZERBAIJAN

Abstract BACKGROUND Medulloblastoma is the most common malignant brain tumor in children, accounting for 20-25% of all pediatric brain tumors. Patients are classified into two prognostic groups. The standard-risk group includes children older than 3 years, with no distant metastases (Chang stage M0), and with minimal residual tumor (<1.5 cm²) after surgery. The high-risk group includes patients under 3 years of age, those with metastatic disease, or those who underwent only partial tumor resection. MATERIAL AND METHODS Between 2012 and 2022, a total of 50 children were treated for medulloblastoma, with a mean age of 12 years. All patients were treated according to the HIT-2000, HIT-2014, and HIT-2020 protocols. Children in the high-risk group received 8 cycles of induction chemotherapy (using carboplatin, etoposide, vincristine, cyclophosphamide, and high-dose methotrexate at a reduced dose of 1 g/m², instead of the standard 5 g/m²). This was followed by craniospinal radiotherapy (25-30 Gy to the entire CNS with an additional boost to the posterior fossa) and 4 courses of maintenance chemotherapy according to the Parkers protocol (cisplatin, lomustine, and vincristine). RESULTS Most patients tolerated chemotherapy and radiotherapy satisfactorily. Among high-risk patients, 7 experienced recurrence (4 during treatment), and 7 children died. The 10-year event-free survival rate was 56%, which is comparable to international outcomes. Importantly, the reduced methotrexate dose of 1 g/m² did not result in decreased survival. CONCLUSION Our experience suggests that using methotrexate at a reduced dose of 1 g/m² instead of the standard 5 g/m² does not compromise survival in high-risk medulloblastoma patients. This supports the conclusion that the routine use of high-dose methotrexate (5 g/m²) may not be justified, especially considering its toxicity and limited resource settings.