Treatment patterns for extramedullary multiple myeloma and outcomes with CAR-T therapy and bispecific antibodies.

person Saurabh Zanwar Mayo Clinic, Rochester, MN info_outline Saurabh Zanwar, Matthew Ho, Prashant Kapoor, Moritz Binder, Francis Buadi, Angela Dispenzieri, David Dingli, Amie L. Fonder, Morie A. Gertz, Wilson I. Gonsalves, Suzanne R. Hayman, Yi Lisa Hwa, Miriam A. Hobbs, Taxiarchis Kourelis, Martha Lacy, Nelson Leung, Eli Muchtar, Rahma M. Warsame, S. Vincent Rajkumar, Shaji Kumar

Authors person Saurabh Zanwar Mayo Clinic, Rochester, MN info_outline Saurabh Zanwar, Matthew Ho, Prashant Kapoor, Moritz Binder, Francis Buadi, Angela Dispenzieri, David Dingli, Amie L. Fonder, Morie A. Gertz, Wilson I. Gonsalves, Suzanne R. Hayman, Yi Lisa Hwa, Miriam A. Hobbs, Taxiarchis Kourelis, Martha Lacy, Nelson Leung, Eli Muchtar, Rahma M. Warsame, S. Vincent Rajkumar, Shaji Kumar Organizations Mayo Clinic, Rochester, MN, Mayo Clinic (Rochester, MN), Rochester, MN, Mayo Clinic Department of Pediatric and Adolescent Medicine, Rochester, MN, Division of Hematology, Mayo Clinic, Rochester, MN Abstract Disclosures Research Funding No funding received None. Background: Extramedullary Multiple Myeloma (EMM) is an aggressive entity with a dismal prognosis. Immune effector therapies (IETs), including chimeric antigen receptor T-cell (CAR-T) therapies and bispecific T-cell engaging antibodies (BsAb), have demonstrated excellent efficacy in relapsed/refractory MM with limited data for efficacy in EMM. Here, we report the treatment outcomes for patients with EMM. Methods: We identified 299 patients with EMM diagnosed between 01/01/2000 and 12/31/2021 after excluding solitary plasmacytomas, paraskeletal MM and primary plasma cell leukemia. The IMWG criteria were used for response definition. Results: Of the 299 patients, 204 (68%) patients had secondary EMM (sEMM) and 95 (32%) patients had primary EMM (pEMM). For sEMM (n=204), the median progression free survival (PFS) with initial therapy was 2.9 (95% CI: 2.4-3.2) months. Initial treatment strategies for sEMM were heterogenous and demonstrated in the table; 44% patients achieved ≥partial response (PR) with initial treatment for sEMM. The median PFS in patients with ≥PR was 5.8 (95%CI: 4.5-6.9) months vs 1.8 (95%CI: 1.4-2; p <0.0001) months for <PR. For patients with pEMM (n=95), the median PFS was 12.9 (95% CI: 6.7-18) months; the median PFS was 17.4 (95%CI: 12.9-25.4) months for patients with ≥PR versus 1 month (95%CI: 0.8-2) in patients with <PR. Thirty patients (all sEMM and triple class refractory) were treated with IET after development of EMM: 18 with BCMA-directed CAR-T, 10 with BsAbs, and 2 with both CAR-T and BsAbs. In patients receiving CAR-T therapy, 75% (15/20) achieved ≥PR with 40% (n=8) achieving MRD negative (by flowcytometry) complete response. Fifteen (75%) patients receiving CAR-T had progressive disease (PD); 7 with systemic and EMM PD and 4 patients each with isolated EMM or systemic PD. The median PFS for patients treated with CAR-T was 4.9 months [3.1- not reached (NR)]. Among patients achieving a ≥PR with CAR-T, the median PFS was 5.8 (95%CI: 4.7-NR) months vs 1.4 months [(95%CI: 0.8-NR), p<0.001] for <PR. Among patients treated with BsAbs (10-BCMA, 1 each against FcRH5 and GPRC5D), 33% (4/12) achieved a ≥PR. Ten (83%) patients had PD on BsAb; 8 with both EMM and systemic PD and 1 patient each with isolated EMM or PD. The median PFS with BsAb was 2.9 months (95%CI: 2.2-NR). Conclusions: Patients with EMM continue to have dismal outcomes with conventional therapies. High response rates were noted with CAR-T therapy, but these tend to be short-lived. PFS with initial treatment for secondary EMM. Groups n Median PFS (95%CI), months P value Proteasome Inhibitor (PI) plus IMiD based combination without CD38 antibody(Ab)] 24 2.2 (1.9-5.2) 0.078 CD38 Ab-combination (including with PI or IMiD) 36 4.5 (2.5-7.6) CAR-T or BsAb 12 3.9 (1.9-NA) VDT-PACE like and alkylator combinations 59 2.9 (2.4-3.5) Either PI or IMiD-based combination without CD38 Ab 34 3.1 (2.2-5.1) Other therapies 13 1.5 (0.8-NA)