Amyloidogenic serum free light chains (sFLC) drive disease progression in AL amyloidosis. Matrix-assisted laser desorption/ionization-time of flight mass spectrometry-based free light chain assay (FLC-MS) has greater sensitivity than conventional sFLC assays allowing for the detection of serological residual disease. We report the utility of FLC-MS in a large series of patients with AL amyloidosis assessing the impact of FLC-MS negativity after treatment on overall survival and organ …