Venetoclax-Dexamethasone in Relapsed and/or Refractory t(11;14) Amyloidosis

The purpose of this study is assess safety, safest dose, and effectiveness of venetoclax in combination with dexamethasone in participants with t(11;14) positive relapsed (comes back) or refractory (did not get better) light chain amyloidosis.

Inclusion Criteria: * Age ≥ 18 years at time of signing Informed Consent Form * Ability to comply with the study protocol, in the investigator's judgment * Confirmed diagnosis of systemic AL amyloidosis by mass spectrometry or immunohistochemistry (IHC) on a tissue biopsy * Has received ≥1 prior lines of therapy, including an anti-cluster of differentiation 38 (CD 38) monoclonal antibody * Participants with a history of autologous hematopoietic cell transplantation must have recovered from any transplant-related toxicities * Presence of t(11;14) on FISH at any time since diagnosis (Eligibility must confirmed by FISH testing at Columbia University Irving Medical Center (CUIMC) * Eastern Cooperative Oncology Group (ECOG) performance status of 0, 1, or 2 Exclusion Criteria: * Known hypersensitivity to any of the study drugs * History of other malignancy that could affect compliance with the protocol or interpretation of results (Patients with a history of curatively treated basal or squamous cell carcinoma of the skin, in situ carcinoma of the cervix, breast cancer, or Hodgkin's Lymphoma are generally eligible. Patients with a malignancy that has been treated, but not with curative intent, will be excluded, unless the malignancy has been in remission without treatment for ≥ 2 years prior to enrollment.) * Evidence of other clinically significant uncontrolled condition(s) including, but not limited to, uncontrolled systemic infection (viral, bacterial, or fungal) * Patients on renal replacement therapy * Known GI disease or GI procedure that could interfere with oral absorption (including difficulty swallowing) * New York Heart Association (NYHA) Class III or IV heart failure * Mayo stage three-B (IIIB) with N-terminal pro-hormone B-type natriuretic peptide (NT-Pro BNP) \> 8500 pg/mL * Prior exposure to anti-apoptotic protein B-cell lymphoma 2 (BCL-2) inhibitors * Patients with human immunodeficiency virus (HIV) who are not on highly active antiretroviral therapy (HAART) or those with active hepatitis A, B, or C infection * Patients meeting criteria for symptomatic multiple myeloma by one of the following:(a) Lytic lesions on imaging (b) Plasmacytoma, (c) Hypercalcemia without any alternate etiology, or (c) Bone marrow plasma cell infiltrate of greater than 60%