Implications of ¹⁸F-FDG PET/CT findings before autologous stem cell transplant in patients with multiple myeloma.

e20023 Background: The IMWG recommends using 18 F-FDG PET/CT (PET) to monitor response to therapy in multiple myeloma (MM). Prior studies in patients who received chemotherapy before autologous stem cell transplant (ASCT) found that severe FDG uptake on PET was associated with inferior event free survival. However, novel agents and monoclonal antibodies have changed the landscape of MM and chemotherapy is no longer used as initial treatment making the role of PET before ASCT unclear. This study explores findings on pre-ASCT PET that may predict shorter remissions after ASCT. Methods: This was a retrospective cohort study. Patients were included if they had a PET at least 60 days before ASCT between 2014 and 2021. All patients achieved at least a partial response (PR) prior to ASCT. The primary endpoint, PFS was defined as time to progression on labs, imaging or bone marrow biopsy necessitating change in therapy or resulting in death after ASCT. The cytogenetic risk category (CG), number of bone lesions at diagnosis, presence of severe FGD uptake on PET (defined as SUV max ≥ 4.2) and persistence of lesions on PET was recorded. Patients who did not experience the event of interest were censored at their last date of clinic follow up. Hazard ratios (HR) for disease progression were estimated using Cox proportional hazards models. Results: 151 patients were included in our study. All patients underwent induction with a 3-drug regimen containing a proteasome inhibitor (PI) and/or an immunomodulatory agent (IMiD). 32% had high risk CG, 44% had > 3 bone lesions at diagnosis, 24% had severe FDG uptake and 29% had > 3 lesions on pre-ASCT PET. The presence of high-risk CG [HR 2.08 (1.03 – 4.17)] and severe FDG uptake on diagnostic PET [HR 6.43 (2.58 – 16.07)] was associated with more aggressive disease and shorter PFS. Patients with > 3 lesions in their pre-transplant PET had a statistically significant decreased PFS [HR 2.01 (1.02 – 3.96)] compared to those with ≤ 3 lesions. Conclusions: This study found that that persistence of > 3 lesions on pre-ASCT PET were an adverse finding associated with an increased risk of progression. To our knowledge these findings have not previously been shown in patients treated with PIs and IMiDs before ASCT. Significantly shorter PFS was observed in patients with high-risk CG and severe FDG uptake on initial PET, consistent with our knowledge of MM. In addition to established risk factors for aggressive disease, persistence of > 3 bone lesions on PET/CT could be used to identify a high-risk group of patients who may benefit from more intensive surveillance or therapy after ASCT. [Table: see text]