P12.35.B A CASE OF RARE CONCURRENT GLIOBLASTOMA AND DIFFUSE LARGE B-CELL LYMPHOMA: SUCCESSFUL TREATMENT WITH NO EVIDENCE OF GLIOBLASTOMA PROGRESSION

Abstract BACKGROUND The simultaneous occurrence of glioblastoma multiforme (GBM) and diffuse large B-cell lymphoma (DLBCL) is an exceptionally rare clinical presentation. This case highlights the challenges of managing two aggressive malignancies in a patient, focusing on the stable course of GBM during the treatment of DLBCL. CASE PRESENTATION A 38-year-old female presented in July 2023 with neurological symptoms, including headache, anisocoria, and right-sided weakness. Magnetic resonance imaging (MRI) revealed a 5.5 cm × 4.5 cm × 5 cm well-defined hypodense lesion in the left frontal lobe, with rim enhancement on post-contrast imaging. Surgical resection was performed in August 2023, and histopathological and molecular analysis confirmed the diagnosis of GBM with methylation of the MGMT promoter region, a finding typically associated with a more favorable prognosis. The patient then began standard treatment with radiotherapy and temozolomide chemotherapy according to the Stupp regimen, continuing until March 2024. In March 2024, suspected progression of the GBM prompted a switch to dose-dense temozolomide. During this period, in December 2024, a new mass was detected in the left cervical region. Biopsy results confirmed the diagnosis of DLBCL, which exhibited an activated B-cell (ABC) phenotype, MYC translocation, CD20 positivity, and a high proliferative index (100%). A revision of the brain tumor biopsy was requested, and GBM was confirmed once again. The lymphoma was localized to the left neck and submandibular region, classified as stage IA, with an International Prognostic Index (IPI) of 0. Given the diagnosis of DLBCL, the patient completed her temozolomide therapy and transitioned to the R-DA-EPOCH regimen (Rituximab, dose-adjusted Etoposide, Prednisone, Vincristine, Cyclophosphamide, and Doxorubicin). The patient completed four cycles of R-DA-EPOCH, during which she experienced grade 4 febrile neutropenia after each cycle, which was managed with appropriate supportive care. In addition, the patient received two cycles of intrathecal chemotherapy, with cerebrospinal fluid showing no malignant cells. OUTCOME Follow-up PET-CT after the final cycle of R-DA-EPOCH demonstrated complete remission of DLBCL. MRI of the brain showed no evidence of residual or recurrent GBM, indicating stable disease. As of the latest follow-up, the patient remains in stable condition with no signs of progression of GBM. CONCLUSION This case illustrates the rare and unique co-occurrence of GBM and DLBCL in the same patient. It also suggests that the treatment for DLBCL with the R-DA-EPOCH chemotherapy regimen may have had a stabilizing effect on the GBM, with no evidence of progression despite initial concerns of GBM recurrence. This case emphasizes the complexity of managing dual malignancies and provides insight into the potential interactions between treatments for different cancers