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4468 A Comparative Study of [18f]FDG PET and MRI for Evaluating Treatment Response in Primary CNS Lymphoma Patients Undergoing High-Dose Methotrexate Therapy

Program: Oral and Poster Abstracts
Session: 626. Aggressive Lymphomas: Clinical and Epidemiological: Poster III
Hematology Disease Topics & Pathways:
Research, Clinical trials, Adult, Lymphomas, Clinical Research, B Cell lymphoma, Diseases, Aggressive lymphoma, Lymphoid Malignancies, Technology and Procedures, Study Population, Human, Imaging
Monday, December 9, 2024, 6:00 PM-8:00 PM

Minyoung Oh1*, Hyungwoo Cho2*, Ji Eun Park3*, Ho Sung Kim3*, Heounjeong Go4*, Chan-Sik Park, MD, PhD4*, Sang-wook Lee5*, Sang Woo Song6*, Young-Hoon Kim6*, Young Hyun Cho7*, Seok Ho Hong6*, Jeong Hoon Kim6*, Dong Yun Lee8*, Jin-Sook Ryu9*, Dok Hyun Yoon, MD, PhD2 and Jae Seung Kim8*

1Department of Nuclear Medicine, Asan Medical Center, University of Ulsan College of Medicine, Songpa-Gu, South Korea
2Department of Oncology, Asan Medical Center, University of Ulsan College of Medicine, Seoul, Korea, Republic of (South)
3Department of Radiology, Asan Medical Center, University of Ulsan College of Medicine, Seoul, Korea, Republic of (South)
4Department of Pathology, Asan Medical Center, University of Ulsan College of Medicine, Seoul, Korea, Republic of (South)
5Department of Radiation Oncology, Asan Medical Center, University of Ulsan College of Medicine, Seoul, Korea, Republic of (South)
6Department of Neurological Surgery, Asan Medical Center, University of Ulsan College of Medicine, Seoul, Korea, Republic of (South)
7Department of Neurological Surgery, Asan Medical Center, University of Ulsan College of Medicine, Seoul, Korea, Republic of (South)
8Department of Nuclear Medicine, Asan Medical Center, University of Ulsan College of Medicine, Seoul, Korea, Republic of (South)
9Department of Nuclear Medicine, Asan Medical Center, University of Ulsan College of Medicine, Seoul, Korea, Republic of (South)

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 (5 CR and 19 PR on MRI at the interim) demonstrated CMR on [18F]FDG brain PET/CT at the interim analysis. Of note, none of the patients who achieved CMR at interim PET/CT showed disease progression on MRI or PET/CT at the end of treatment response analysis. At the end-of-treatment evaluation, MRI results showed 27 patients with CR, 7 with CRu, 10 with PR, and 4 with PD. There were no statistical differences in predicting survival outcomes between CR, CRu, and PR on MRI at the end of treatment with a 1-year PFS rate of 87.7% (95% CI: 74.7% - 100.0%), 66.7% (95% CI: 29.1% - 100.0%) and 87.5%% (95% CI: 64.6% - 100.0%), respectively (p = 0.311). On the other hand, 44 patients showed CMR on [18F]FDG brain PET/CT at the end of treatment, which was associated with a better 1-year PFS (82.1% [95% CI: 70.1% vs. 94.1%] vs. 0.0% [95% CI was not calculable], p < 0.001).

Conclusion:

In patients with PCNSL, response evaluation with MRI at the interim and end of treatment did not significantly differ in predicting survival outcomes. However, achieving CMR on [18F]FDG brain PET/CT at the end of treatment is associated with more favorable PFS. While interim PET shows potential as a prognostic indicator, further study is needed to establish its role. Our findings suggest a potential utility of [18F]FDG PET/CT in evaluating responses for patients with PCNSL. The results of the final analysis will be available upon completion of the study.

Disclosures: Yoon: Abbvie, Abclon, Beigene, BMS, GI cell, GI innovation, GC cell, Verismo, Janssen, Lilly, Novartis, Roche, and Pharos Bio: Consultancy; Asan Medical Center, University of Ulsan College of Medicine: Current Employment; Abbvie, Beigene, Boryung, Celltrion, Kyowa Kirin, Janssen, Samyang and Sanofi: Honoraria, Research Funding; Regeneron: Membership on an entity's Board of Directors or advisory committees.

*signifies non-member of ASH