A Study of the Combination of Talquetamab and Teclistamab in Participants With Relapsed or Refractory Multiple Myeloma

The purpose of this study is to identify the recommended Phase 2 regimen(s) (RP2R\[s\]) and schedule for the study treatment (Part 1), to characterize the safety of the RP2R(s) for the study treatment (Part 2) and to evaluate the anticancer activity of talquetamab + teclistamab in participants with relapsed or refractory multiple myeloma and extramedullary disease (EMD) (Part 3).

Inclusion Criteria: * Documented initial diagnosis of multiple myeloma according to International Myeloma Working Group (IMWG) diagnostic criteria * Part 1 and 2: Participant could not tolerate or has disease that is relapsed or refractory to established therapies, including the last line of therapy. Part 3: (a) Relapsed or refractory disease, and exposed to a PI, IMiD, and an anti-CD38 mAb; (b) Documented evidence of progressive disease based on investigator's determination of response by IMWG criteria on or after their last regimen * Part 1 and Part 2: Eastern Cooperative Oncology Group (ECOG) performance status grade of 0 or 1 at screening and immediately before the start of study drug administration. Part 3: ECOG performance status grade of 0, 1, or 2 at screening and immediately before the start of study drug administration Exclusion Criteria: * All Parts: Targeted therapy, epigenetic therapy, or treatment with an investigational treatment or an invasive investigational medical device within 21 days or at least 5 half-lives, whichever is less. Part 3: prior BCMA targeted bispecific antibody therapy; prior GPRC5D targeted therapy * All Parts: Allogeneic stem cell transplant within 6 months before the first dose of study treatment. * All Parts: Central nervous system involvement or clinical signs of meningeal involvement of multiple myeloma. * All Parts: Active plasma cell leukemia (greater than \[\>\]2.0\*10\^9/L plasma cells by standard differential), Waldenström's macroglobulinemia, POEMS syndrome (polyneuropathy, organomegaly, endocrinopathy, M- protein, and skin changes), or primary amyloid light chain amyloidosis