Teclistamab In Waldenstrom's Macroglobulinemia

The goal of this clinical trial is to assess the efficacy of teclistamab in participants with relapsed or refractory Waldenstrom's macroglobulinemia who have received prior therapy. This study also aims to assess the safety and tolerability of teclistamab, how quickly and to what extent response is seen in participants, how strong any clinical benefit of teclistamab might be, and determine the response to teclistamab based on the combination of MY88 and CXCR4 mutations. The main questions it aims to answer are: * Will teclistamab be effective in treating Waldenstrom's macroglobulinemia? * By targeting BCMA with teclistamab, will direct Waldenstrom's macroglobulinemia tumor death occur? Participants will receive teclistamab for up to 9 cycles (cycle 1 is 14 days, cycles 2-5 are 28 days, and cycles 6-9 are 56 days) or until their disease progresses, another illness or change in their condition prevents them from further receiving the treatment, they experience unacceptable side effects, they demonstrate an inability or unwillingness to receive the medication regimen, or they decide to withdraw from the study. Participants will be followed for up to 3 years from the last treatment.

Inclusion Criteria: * Clinicopathological diagnosis of WM per IWWM2 criteria. * Meeting criteria for treatment per IWWM2 criteria. * Relapsed or refractory WM with at least 1 prior line of treatment, including an anti-CD20 monoclonal antibody containing regimen or a BTK inhibitor. * Patients should have received a prior BTK inhibitor (except for contraindications such as bulky disease, amyloidosis, significant medication interactions, or a history of severe bleeding). * Participants with suspected or symptomatic hyperviscosity (e.g. nosebleeds, headaches, blurred vision) must undergo plasmapheresis prior to treatment initiation. * Adults aged ≥18 * ECOG performance status ≤2 (Karnofsky ≥60%, see Appendix A) * A female participant of childbearing potential must have a negative highly sensitive serum pregnancy test at screening and again either a serum or urine pregnancy test within 24 hours of the start of study treatment and must agree to further serum or urine pregnancy tests during the study. * A female participant must be: * Not of childbearing potential, or * Of childbearing potential and practicing at least 1 highly effective method of contraception * A male participant must wear a condom (with or without spermicidal foam/gel/film/ cream/suppository) when engaging in any activity that allows for passage of ejaculate to another person during the study and for 3 months after receiving the last dose of study treatment. * Participants must meet the following organ and marrow function as defined below: * Absolute neutrophil count ≥500/mcL; the patient may enroll below this threshold if neutropenia is believed to be caused by WM bone marrow involvement. Growth factors are not permitted \