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988 Management and Outcomes for Primary Mediastinal B-Cell Lymphoma Patients with Partial Metabolic Response

Program: Oral and Poster Abstracts
Type: Oral
Session: 627. Aggressive Lymphomas: Clinical and Epidemiological: Uncommon Aggressive NHL
Hematology Disease Topics & Pathways:
adult, Clinical Practice (Health Services and Quality), Diseases, Therapies, Lymphoid Malignancies, Study Population, Human
Monday, December 11, 2023: 5:15 PM

David Hodgson, MD1*, Mahmood Aminilari, PhD1*, Donna Liao, MD2*, Xiang Y Ye, PhD3*, Ur Metser, MD, FRCPC4*, Michael Crump, MD5*, John Kuruvilla, MD1*, Abi Vijenthira, MD, MS6, Vishal Kukreti, MD, FRCP, MSc6, Robert Kridel7, Richard Tsang, MD8*, Sita D. Bhella, MD, MSc9*, Danielle Rodin, MD1* and Anca Prica, MD, MSc6*

1Princess Margaret Cancer Centre, Toronto, ON, Canada
2Department of Radiation Oncology, University of Toronto, Toronto, ON, Canada
3Biostatistics, Princess Margaret Cancer Centre, Toronto, ON, Canada
4Department of Medical Imaging, University Health Network Princess Margaret Hospital, Toronto, ON, Canada
5Department of Medical Oncology and Hematology, Princess Margaret Cancer Centre, Toronro, CAN
6Division of Medical Oncology and Hematology, Princess Margaret Cancer Centre - University Health Network, Toronto, Canada
7Princess Margaret Cancer Centre, University Health Network, Toronto, Canada
8Princess Margaret Hospital, Toronto, ON, CAN
9Division of Medical Oncology and Hematology, Princess Margaret Cancer Centre - University Health Network, Toronto, ON, Canada

Background: The optimal management of patients with primary mediastinal B-cell lymphoma (PMBCL) who experience a partial metabolic response (PMR) on FDG-PET after initial systemic therapy is unclear. This study aimed to investigate different management strategies and outcomes for PMBCL patients who achieved PMR following primary systemic therapy, utilizing a single-center retrospective design.

Methods: We reviewed the electronic medical records of 121 PMBCL patients who underwent post-chemotherapy PET scans at the Princess Margaret Cancer Center, Toronto, from January 2009 to September 2021. Using Modified Lugano criteria (2014), post-chemotherapy PET scan results were evaluated, with Deauville score (DS) 0-3 considered a complete metabolic response. Demographic, clinical, and imaging characteristics of the PMBCL population were analyzed. The Kaplan-Meier method was used to estimate progression-free survival (PFS), measured from the time of the post-systemic therapy PET.

Results: A total of 121 patients with PMBCL underwent post-chemotherapy PET scans. Among them, 49 patients (40%) demonstrated incomplete metabolic response (DS4-5) Among these 49 patients, 12 showed primary refractory disease, while 37 demonstrated a partial metabolic response (PMR, DS4). The median age at diagnosis of the 37 patients with PMR was 30.8 years (range:18.4 – 52.8 years), and 20 (54%) were female. The median length of follow-up for these patients was 3.7 years (range: 0.4 to 9.2 years). Most PMR patients were stage I/II (26 patients, 70.3%), while the remaining were stage III (2 patients, 5.4%), or stage IV (8 patients, 21.6%), and 26 (70.3%) had a large mediastinal mass (maximum diameter exceeding 10cm). Initial systemic treatment was R-CHOP-21 (34 patients, 91.9%), R-CHOP combined with dose-adjusted R-EPOCH (2 patients, 5.4%), and dose-adjusted EPOCH (1 patient, 2.7%). Thirty one patients (83.8%) received 6 cycles.

Following treatment strategies were employed to manage PMR: 1) radiation therapy (RT) only with or without biopsy in 30 patients (80.1%); 2) an observational approach (repeating PET scans without immediate treatment) in 3 patients (8.1%); 3) salvage chemotherapy in 3 patients (8.1%) and other approach in 1(2.7%) patient.

The 2-year progression-free survival (PFS) rate for all patients with incomplete metabolic response (n=49) was 74.5% (95% CI = 62.5% to 88.9%). For patients with primary progression on post-chemotherapy PET scans the 2-year PFS (ie free of 2nd progression) was 40% (18.7% to 85.5%), while the 2-year PFS for patients with PMR was 85.4% (74.3% to 98.1%). PMR patients who underwent radiotherapy (RT) had the 2-year PFS rate of 92.7% (95% CI: 83.5% to 100.0%). No progression or relapsed occurred among the 3 patients with PMR who were managed with repeating PET scans without immediate further treatment.

Conclusion: This study replicates prior work demonstrating a higher rate of incomplete metabolic response for PMBCL patients following R-CHOP-21 than typically reported for DLBCL. RT to persistent PET-avid sites is associated with excellent PFS. The favorable outcome of PMR patients without any additional treatment illustrates the non-trivial risk of false-positive PET scans following systemic therapy, and the need to identify criteria that can distinguish those who need additional treatment from those who can be safely observed.

Disclosures: Kuruvilla: Abbvie, BMS, Gilead, Merck, F. Hoffmann-La Roche Ltd, Seattle Genetics: Consultancy; F. Hoffmann-La Roche Ltd, Astra Zeneca, Merck: Research Funding; Abbvie, Amgen, AstraZeneca, BMS, Genmab, Gilead, Incyte, Janssen, Merck, Novartis, Pfizer, F. Hoffman-La Roche Ltd, Seattle Genetics: Honoraria; Karyopharm: Other: DSMB. Bhella: Gilead: Speakers Bureau; Novartis: Speakers Bureau. Prica: Kite Gilead: Honoraria; Abbvie: Honoraria; Astra-Zeneca: Honoraria.

*signifies non-member of ASH