P887: prognostic value of positron emission tomography/computed tomography in relapsed/refractory multiple myeloma patients treated with chimeric antigen receptor t-cell therapy

Topic: 14. Myeloma and other monoclonal gammopathies - Clinical Background: Chimeric antigen receptor (CAR) T-cells, mainly those targeting the B-cell maturation antigen (BCMA), are an effective treatment for relapsed/refractory multiple myeloma (RRMM) patients. Unfortunately, a significant number of patients relapse during the first two years. The predictive value of positron emission tomography/computed tomography (18FDG-PET/CT) in this group of patients has not been established. Aims: To determine if 18FDG-PET/CT is useful for risk prediction in RRMM patients that receive BCMA-targeting CAR-T cell therapy. Methods: Fifty-seven patients received CAR-T cell treatment, 55 (96%) targeting BCMA and 2 (4%) targeting SLAMF7, between April 2018 and December 2022. 18FDG-PET/CT was performed at baseline and one month after treatment for all patients. We analyzed the presence of focal lesions (FL), uptake of bone marrow (BM) and FL measured by Deauville score, presence of paramedullary (PMD) and extramedullary disease (EMD), and measurement of total tumor volume (TMTV) and total tumoral glycolysis (TLG). 18FDG-PET/CT was considered positive if Deauville scores >= 4 were found for any of the aforementioned variables. Results: Among 57 baseline exams, 45 (79%) were positive. Table 1 shows the frequency and percentage of the different 18FDG-PET/CT variables with Deauville score >= 4 and how many of the patients’ scans were positive due to the isolated finding of either hypermetabolic BM or FL, PMD or EMD, or only EMD. The information was obtained at baseline and one month after CAR-T cell infusion (early disease assessment). The presence of baseline EMD was associated with significantly shorter PFS (median 3.7 months [95%CI 0.9 - 6.4] versus 12.2 months [95%CI 9.1 - 15.3]) (P <.001) and OS (median 7.3 months [95%CI 0.01 - 19.2] versus 25.2 months (95%CI 17.4 – 32.9); P =.002); with a hazard ratio (HR) of 5.3 (95%CI 2.1 - 13.3; P <.001) and 3.9 (95%CI 1.5 – 9.9; P =.004) for PFS and OS, respectively. Fifty-six patients were available for early disease assessment. A total of 33 (59%) scans remained positive, and 2 (4%) previously negative scans became positive. Persistent EMD was associated with significantly shorter PFS (0.9 months [95%CI 0.4 – 1.5] vs 12.0 months [95%CI 7.2 – 16.8]) (HR 15.2 (95%CI 3.8 – 59.9; P <.001) and OS (2.6 months [95%CI 1.8 – 3.4] vs 20.9 months [95%CI 13.4 – 28.4]) (HR 38.4 [95%CI 6.2 – 237.6; P <.001]). Conversely to the basal scans, the persistence of hypermetabolic PMD is also associated with significantly shorter PFS (median of 4.6 months [95%CI 0.9 – 8.4] vs 12.2 months [95%CI 7.6 – 16.9] (P =.02)) (HR 2.2 [95%CI 1.1 – 4.3; P <.023]); but not OS (P =.067). The presence of hypermetabolic FL or BM uptake with Deauville score >=4 has no significant impact on PFS or OS, neither at baseline nor after early assessment. Summary/Conclusion: Baseline presence of EMD detected by PET-CT is associated with shorter PFS and OS. The persistence of PMD or EMD after early assessment in RRMM patients treated with CAR-T cell therapy associates with shorter PFS and OS. PET findings with Deauville score >=4 Baseline (N = 57) 1 month after CAR-T (N = 56) BM 27 (47%) 22 (39%) FL 41 (72%) 27 (48%) PMD 25 (44%) 14 (25%) EMD 7 (12%) 3 (5%) PET is positive due to Baseline (N = 45) 1 month after CAR-T (N = 35) Only BM/ FL 19 (42%) 21 (60%) PMD/ EMD 26 (57%) 14 (40%) Only EMD 1 (1%) 1 (2%) Keywords: Prognostic factor, FDG-PET, CAR-T, Multiple myeloma