P-002: Impact of Bridging Therapy (BT) on outcome of Relapsed Refractory Multiple Myeloma (RRMM) with Ide-cel CAR T-cell therapy: Real-world Experience from the U.S. Myeloma CAR T Consortium

Introduction: Ide-cel is an FDA-approved treatment for RRMM patients (pts). However, there is limited data on how BT for disease control during its manufacturing process affects clinical outcomes.

Methods: Eleven US academic centers contributed data to this analysis without involvement from the manufacturer. By 5/1/2022, 235 pts had undergone leukapheresis, with 214 infused with a median follow up of 9 months (mos). BT was given between leukapheresis and CAR-T infusion.

Results: In this analysis, 79% of pts (n=170) received BT, which included alkylator-based in 35.5%, steroid and or IMiD/Ab combos (IMiD combos) in 14%, PI combinations (PI combos) in 12%, and selinexor in 10%. BT recipients had higher ECOG PS 2-4, R-ISS 2-3, ferritin, and CRP before lymphodepleting (LD) chemo, however, no difference among BT subgroups. No difference in prior lines of therapy or penta-refractory between BT and No BT (NBT) groups or BT subgroups. Median cycle of the BT was 1 (1-7), with overall response rate (ORR) of 12%, with no difference among BT subgroups. Incidence and severity of CRS and ICANs were comparable in BT and NBT. However, pts who received BT had a longer median hospital stay compared to NBT, particularly in the alkylator/selinexor subgroups. There were no significant difference in cytopenias at day 90 post CAR-T between the BT and NBT or BT subgroups. For the 73% (n=157) evaluable for day 90 response, there was no difference in the complete or ORR between the BT and NBT groups (41% vs. 52%; p=0.2 and 84% vs. 87.5%, p=0.8, respectively). Median PFS was worse at 8.1 mos in BT vs 11.5 mos in NBT (p=0.03). Among BT subgroups, PFS was the longest with IMiD combos with median PFS not reached (NR), comparable to NBT, and was significantly longer than all other BT subgroups (p=0.01). The median OS was 13.8 mos with BT and NR in NBT (p=.002). In BT subgroup analysis, alkylators group had a shorter OS, although, this was not significant (p=.06). There was no significant difference in PFS and OS in relationship to response to BT (p=.6 and p=.9, respectively).

Conclusions: Pts without BT had longer PFS and OS post ide-cel, likely reflective of less aggressive disease. Those who received BT with steroid/IMiD and Ab combos had similar PFS as NBT. However, BT choice is complicated by disease severity and should be evaluated per patient circumstances.