Evaluation of minimal residual disease using next-generation flow cytometry in patients with AL amyloidosis

The treatment of light chain (AL) amyloidosis aims to completely eliminate the toxic light chain production, as assessed by sensitive serum- or urine-based methods such as immunofixation and free light chain (FLCs) quantification. Complete hematologic responses (hemCR) can be achieved in a significant proportion of patients with AL, either with conventional therapies or with high-dose melphalan, and are associated with better overall survival and improved organ function. However, hematologic relapses still occur and organ function may continue to deteriorate due to small residual clones that may lead to disease recurrence and/or may produce very small amounts of toxic light chains which are undetectable by conventional techniques. Next-generation flow cytometry (NGF) is a very sensitive method for the evaluation of minimal residual disease (MRD) and one of the standard methods for the assessment of MRD in patients with multiple myeloma (MM), reflected in the new response assessment criteria2. Patients with MM who are negative for MRD have significantly improved progression-free and overall survival, even among those who have achieved a CR3,4. Such data are sparse in patients with AL amyloidosis, although the presence of MRD may prove a crucial factor for delayed organ response or deterioration of organ function despite conventional hemCR. The aim of the current study was to evaluate feasibility and applicability of MRD by NGF in patients with AL at hemCR.