Primary AL amyloidosis PCs are significantly more susceptible to Btz toxicity than primary MM PCs. Primary PCs were purified by double immunomagnetic positive (CD138) selection from BM biopsies obtained from patients diagnosed with systemic light chain (AL) amyloidosis (n = 10) and MM (n = 8), seeded in multiwell plates and treated with increasing doses of Btz for 24 hours. Apoptotic responses were assessed by flow cytometric analysis, upon labeling with propidium iodide, fluorescent-conjugated anti-syndecan 1 antibody and annexin V. The graph shows each patient’s average EC₅₀, and each group’s mean ± standard error. *P < .05 (Student t test).