The outcomes of patients (pts) with triple and pentaclass relapsed refractory multiple myeloma (RRMM) are poor. B-cell maturation antigen (BCMA) chimeric antigen receptor T-cell (CAR T) therapy in RRMM has been approved since March 2021. Early re-emergence of soluble BCMA may be a prognosticator for clinical relapse. The objective is to trend re-emergence of BCMA at 3 months and 6 months using multiparameter flow cytometry (MFC) from bone marrow (BM) aspirate or biopsy to compare outcomes between BCMA CAR T products. The study is a prospective cohort study that includes RRMM patients who received BCMA CAR T at the University of Kansas Health System over the last 2 years, followed at intervals of 3 months. The study setting was conducted at the University of Kansas Health System requiring both inpatient and outpatient care. A total of 56 pts who received BCMA CAR T therapy recipients for RRMM at the University of Kansas Health System between May 2021 and May 2023 were included. Those with less than 3 months of follow-up were excluded from the analysis. All patients had standard procedure of BM evaluation at 1 3 and 6 months, and 1 year. Eight-color MFC was performed on the BM specimens. Responses were evaluated using the International Myeloma Working Group criteria. BCMA re-emergence was defined as BCMA greater than nadir on either polyclonal or monoclonal BM plasma cells. Fifty-six pts were included in the analysis, of which 38 received ide-cel and 18 received cilta-cel. A greater proportion of ide-cel patients had cumulative re-emergence of BCMA within 12 months post-CAR T compared to cilta-cel patients (58% vs 17%, P=0.004). However, the possible limitation is that there was a significant difference in follow-up time between ide-cel and cilta-cel patients that could explain this difference (11 vs 4 months, P=0.004). There are possible differences in re-emergence of BCMA in different BCMA-CAR T products. This is an early observation and we need more patient enrollment and longer follow-up to develop a final conclusion, which is the next step of our group.