Efficacy of Subsequent Therapies in Multiple Myeloma Patients after Progression on a BCMA Targeting Therapy: A Single-Center Experience
Authors: Paul Barry , Robinson Myra , Cassetta Kristen , Slaughter Daniel , Robinson Jordan , Ndiaye Ami P , Bhutani Manisha , Voorhees Peter M. , Usmani Saad Z. , Atrash Shebli 
Published: November 2020

Background: Targeting B-cell maturation antigen (BCMA) with antibody-drug conjugates (ADCs), bispecific antibodies, or chimeric antigen receptor t-cells (CAR-Ts) has proven safe and effective in recent clinical trials, but relapses remain common. As most patients treated with BCMA targeting therapies are refractory to conventional anti-myeloma therapies, management of these patients poses unique challenges once they progress, with no data available to guide subsequent therapies.
Methods: We performed a retrospective chart review of all relapsed refractory multiple myeloma (RRMM) patients at our institution who progressed while on or after a BCMA targeting therapy and were treated with subsequent therapies. We evaluated the best response achieved and overall survival (OS) measured from progression on BCMA targeting therapies. Kaplan Meier methods were used to estimate OS curves and landmarks between classes of BCMA targeting therapy received (ADC, bispecific antibody or CAR-T), and by type of subsequent therapy.
Results: At a median follow up of 6 months, a total of 47 patients were treated with a BMCA targeting therapy. Of those, a total of 21 (44.7%) patients have progressed, with 18 (38.3%) receiving another therapy. Twelve-month overall survival of the patients who received a subsequent treatment was 51.1% (figure 1a), but varied considerably based on the class of BCMA therapy they received (figure 1b). Patients who progressed after a BCMA CAR-T had the best OS (N =2, 6 mo OS: 100%, 12 mo OS:
Of the 18 patients who progressed and were treated with subsequent therapies, 7 (38.9%) received 2 lines of therapy, 5 (27.8%) received 3 lines of therapy, and 1 patient (5.6%) received 5 lines of therapy. In the first relapse, 4 (22.2%) patients received infusional chemotherapy with CAR-D PACE or CAR-DCEP, 4 (22.2%) received the combination of elotuzumab, pomalidomide, and dexamethasone (Elo-Pd; one of which was first treated with CAR-DCEP), 3 (16.7%) received selinexor based regimens.
The best response seen after first-line post BCMA treatment was a partial response (PR) in 5 (27.8% of patients), whereas 8 (61.5%) patients who received second-line treatment post-BCMA therapy had a PR or better, including 3 (23.1%) who had a very good partial response (VGPR). In the third line post-BCMA, 1 (16.7%) had a VGPR, while 1 (16.7%) had stable disease as their best response. The use of Elo or Dara after anti-BCMA progression seemed to correlate with improved OS (see figure 1c below). While all these patients were Elo naïve, the majority (94.4%) were previously Dara exposed.
Conclusions: Our data demonstrate that many RRMM patients who progress on BCMA targeting therapies still derive benefit from subsequent treatment. Early evidence from our experience suggests a survival advantage with monoclonal antibody-based therapies even in patients who had previously been exposed to these agents-suggesting a possible resensitization with BCMA directed therapy. Although our dataset is a single-center experience, to our knowledge it represents the first report of post-BCMA exposed management of RRMM and provides valuable insight into the treatment of this challenging and ever-expanding population.

Disclosures
Paul: Bristol-Myers Squibb: Other: Stock Ownership (prior employee); Amgen: Consultancy, Speakers Bureau; Regeneron: Membership on an entity's Board of Directors or advisory committees. Bhutani:BMS: Other: Clinical trial funding to institute, Speakers Bureau; Takeda: Other: Clinical trial funding to institute, Speakers Bureau; Prothena: Other: Clinical Trial Funding to Institute; Amgen: Speakers Bureau; MedImmune: Other: Clinical Trial Funding to Institute; Sanofi Genzyme: Consultancy; Janssen: Other: Clinical Trial Funding to Institute. Voorhees:Adaptive Biotechnologies: Other: Personal fees; Bristol-Myers Squibb: Other: Personal fees; Celgene: Other: Personal fees; Janssen: Other: Personal fees; Novartis: Other: Personal fees; Oncopeptides: Other: Personal fees; TeneoBio: Other: Personal fees; Levine Cancer Institute, Atrium Health: Current Employment. Usmani:Celgene: Other; Janssen: Consultancy, Honoraria, Other: Speaking Fees, Research Funding; SkylineDX: Consultancy, Research Funding; Seattle Genetics: Consultancy, Research Funding; Merck: Consultancy, Research Funding; Incyte: Research Funding; Pharmacyclics: Research Funding; Array Biopharma: Research Funding; GSK: Consultancy, Research Funding; Takeda: Consultancy, Honoraria, Other: Speaking Fees, Research Funding; Sanofi: Consultancy, Honoraria, Research Funding; Abbvie: Consultancy; BMS, Celgene: Consultancy, Honoraria, Other: Speaking Fees, Research Funding; Amgen: Consultancy, Honoraria, Other: Speaking Fees, Research Funding. Atrash:BMS, Jansen oncology, Sanofi: Speakers Bureau; Takeda, Amgen, Karyopharm, BMS, Sanofi, Cellactar, Janssen and Celgene: Honoraria; Amgen, GSK, Karyopharm.: Research Funding.