Loncastuximab Tesirine in WM

Inclusion Criteria: * Clinicopathological diagnosis of Waldenström Macroglobulinemia * Symptomatic disease meeting criteria for treatment using consensus panel criteria from the Second International Workshop on Waldenström macroglobulinemia. * At least 2 prior lines of treatment, including an anti-CD20 monoclonal antibody-containing regimen and a BTK inhibitor. * Age 18 years or older * Measurable disease, defined as presence of immunoglobulin M (IgM) paraprotein with a minimum serum IgM level of \> 2 times the upper limit normal. * ECOG performance status ≤2 (Karnofsky ≥60%, see Appendix A) * Women of childbearing potential: Females of childbearing potential (FCBP) must agree to use two reliable forms of contraception simultaneously or have or will have complete abstinence from heterosexual intercourse during the following time periods related to this study: 1) while participating in the study; and 2) for at least 9 months after discontinuation from the study. FCBP must be referred to a qualified provider of contraceptive methods if needed. * Men must agree to use a latex condom during sexual contact with a female of childbearing potential (FCBP) even if they have had a successful vasectomy 1) while participating in the study; and 2) for at least 6 months after discontinuation from the study. * Participants must have normal organ and marrow function as defined below: * Absolute neutrophil count ≥1000/ uL. Growth factors are not permitted \<14 days prior to C1D1. * Plat…