Inclusion Criteria:  Diagnosis of primary AL amyloidosis Relapsed and/or refractory AL amyloidosis Measurable disease Male or female patients 18 years or older Able to give voluntary written consent Eastern Cooperative Oncology Group performance status and/or other performance status 0, 1, or 2. Absolute neutrophil count (ANC) ≥ 1,000/mm3 and platelet count ≥ 75,000/mm3. Total bilirubin ≤ 1.5 × the upper limit of the normal range (ULN). Alanine aminotransferase (ALT) and aspartate aminotransferase (AST) ≤ 3 × ULN. Calculated creatinine clearance ≥ 30 mL/min  Exclusion Criteria:  Non-AL amyloidosis Clinically overt myeloma Prior exposure to Selinexor Clinically significant cardiac disease Severe obstructive airway disease Female patients who are lactating or have a positive serum pregnancy test during the screening period Planned high-dose chemotherapy and autologous stem cell transplantation within 6, 28-day treatment cycles after starting on treatment Failure to have fully recovered (ie, ≤ Grade 1 toxicity) from the reversible effects of prior chemotherapy. Major surgery within 14 days before enrollment. Radiotherapy within 14 days before enrollment. Infection requiring systemic intravenous antibiotic therapy or other serious infection within 14 days before study enrollment. Systemic treatment, within 14 days before the first dose, with strong CYP3A inducers (rifampin, rifapentine, rifabutin, carbamazepine, phenytoin, phenobarbital, see Appendix 11.7), or use of Ginkgo biloba or St. John's wort. Positive for human immunodeficiency virus (HIV), hepatitis B, and hepatitis C Serious medical or psychiatric illness GI disease or GI procedure that could interfere with the oral absorption or tolerance including difficulty swallowing Diagnosed or treated for another malignancy within 2 years before study enrollment or previously diagnosed with another malignancy and have any evidence of residual disease. Patients with nonmelanoma skin cancer or carcinoma in situ of any type are not excluded if they have undergone complete resection. Participation in another clinical trials involving investigational agents within 30 days of starting this trial Peripheral neuropathy (grade 2 with pain or grade 3 or higher).