A Comparative Study of [18f]FDG PET and MRI for Evaluating Treatment Response in Primary CNS Lymphoma Patients Undergoing High-Dose Methotrexate Therapy

• Published in: Blood 2024-11, Vol.144, p.4468-4468
• Main Authors: Oh, Minyoung, Cho, Hyungwoo, Park, Ji Eun, Kim, Ho Sung, Go, Heounjeong, Park, Chan-Sik, Lee, Sang-wook, Song, Sang Woo, Kim, Young-Hoon, Cho, Young Hyun, Hong, Seok Ho, Kim, Jeong Hoon, Lee, Dong Yun, Ryu, Jin-Sook, Yoon, Dok Hyun, Kim, Jae Seung
• Format: Article
• Language: English
• ISSN: 0006-4971
• DOI: 10.1182/blood-2024-198351

Introduction: The standard method for evaluating response in patients with primary central nervous system lymphoma (PCNSL) is T1-weighted contrast-enhanced brain magnetic resonance imaging (MRI). However, brain MRI has limitations in distinguishing between complete response (CR), radiologically unconfirmed complete response (CRu), and partial response (PR) when evaluating treatment responses to predict clinical outcomes. We have previously reported on the role of 18F-fluorodeoxyglucose brain positron emission tomography/computed tomography ([18F]FDG brain PET/CT) in prognostication and response evaluation of PCNSL (Oh and Cho et al, Neuro-oncology 2024). This study aims to prospectively validate the prognostic value of interim responses after two cycles of high-dose methotrexate-based chemotherapy and end-of-treatment responses using [18F]FDG brain PET/CT and MRI in patients with PCNSL undergoing first-line treatment. Patients and methods: From August 2021 to December 2023, 55 newly diagnosed PCNSL patients at Asan Medical Center in South Korea were prospectively enrolled, with ongoing enrollment aiming for a total of 90 patients. All patients received high-dose methotrexate-based chemotherapy as their first-line treatment and underwent [18F]FDG brain PET/CT alongside MRI for response evaluation. [18F]FDG brain PET/CT images were visually assessed as either negative (complete metabolic response: CMR) or positive (showing greater uptake than the contralateral brain or physiological uptake in midline structures) by two nuclear medicine physicians. Results: The median age of the 55 patients was 65 years (range: 28-84) with 26 male participants. With a median follow-up of 14 months (range: 3-33), nineteen patients experienced disease progression. Median progression-free survival (PFS) was not reached. The one-year PFS rate is 71.1% (95% confidence interval [CI]: 58.2% - 84.0%). During treatment, five patients dropped out before the prespecified interim evaluation and seven before the end-of-treatment evaluation due to disease progression, leaving 50 and 48 patients for interim and end-of-treatment response assessment, respectively. At the interim evaluation, MRI results showed 7 patients with CR, 43 with PR, and none with CRu or PD. There was no significant difference in PFS between patients who achieved a CR vs. those who achieved a PR, with a 1-year PFS rate of 51.4% (95% CI: 11.4% - 91.4%) vs. 78.3% (95% CI: 65.7% - 90.9%, p = 0.296). However, 24 patients (