P-182: IMPACT OF MINIMAL RESIDUAL DISEASE IN APHERESIS PRODUCT (aMRD) ASSESSED BY MULTIPARAMETRIC FLOW CYTOMETRY (MFC) IN TRANSPLANT-ELIGIBLE MULTIPLE MYELOMA (MM) PATIENTS

Introduction: The assessment of MRD by MFC in bone marrow (BM) is one of the strongest prognostic factors for predicting progression-free survival (PFS) in MM. Although the presence of aMRD hampers the outcome of patients who underwent autologous stem cell transplantation (ASCT), its value is not completely understood. The aims of the study were to evaluate the prognosis factor associated to aMRD detection and its correlation with response and PFS.

Methods: A retrospective observational study was designed including patients who received ASCT between 2005 and 2023 at the University Hospital of Salamanca. The aMRD evaluation was performed by MFC.

Results: Forty-three (10.4%) of the 414 patients who received ASCT had aMRD +ve. The median age at ASCT was 60 years, 64% were men, 27% ISS-3 and 18% had high risk cytogenetic (HR). No differences were observed between aMRD +ve and -ve patients according to the baseline characteristics.

Ninety percent of the cohort received ASCT in 1^st line, and both aMRD +ve and -ve groups were treated with similar induction schemes, and a similar number of patients received subsequent consolidation and/or maintenance therapy. No differences in aMRD detection were observed based on induction schemes or number of cycles prior to stem cell harvest.

Patients with aMRD +ve achieved poorer responses than those with aMRD -ve before the stem cells harvest (very good partial response or better: 26% vs 68%, P < 0.001). In addition, the presence of aMRD +ve identified patients with poorer responses than those with aMRD -ve: at ASCT (MRD -ve in BM: 0% vs 22%), after ASCT (MRD -ve in BM: 14% vs 51%) and during follow-up (MRD -ve in BM: 23% vs 62%) (all P < 0.001).

With a median follow-up of 56 months, patients with aMRD +ve had significantly lower PFS than those with aMRD -ve (31 vs 58 months, P=0.002). In HR patients, the aMRD -ve did not overcome their poor prognosis and the median PFS was comparable to those patients with aMRD +ve (both 33 months; P=0.679). By contrast, patients with ISS-3 and aMRD +ve experienced shorter median PFS than those with aMRD -ve (18 vs 42 months; P=0.009). Three prognostic groups of patients were established according to aMRD and MRD in BM status before ASCT: aMRD plus MRD +ve in BM (31 months), aMRD -ve plus MRD +ve in BM (49 months, P=0.007) and aMRD plus MRD -ve in BM (72 months, < 0.001). Likewise, the aMRD plus MRD in BM +ve group presented higher probability of early relapse after ASCT (PFS ≤24 months) than the remaining groups: 46% vs 37% vs 35% (both P=0.046).

Conclusions: The response achieved before stem cell harvest was the only prognostic factor associated with the aMRD detection in our series. The presence of aMRD was associated with inferior responses and PFS in patients undergoing ASCT, with a half of them experiencing early relapse. The impact of aMRD according to the different sensitivity reached with MFC, as well as an external comparison with a transplant center that does not perform aMRD, will be presented at the meeting.