Assessment of minimal residual disease using multiparametric flow cytometry in patients with AL amyloidosis.

Despite achieving a hematologic complete response after treatment, many patients with AL amyloidosis do not attain recovery of organ function and/or experience hematologic relapse. A persistent plasma cell clone producing amyloidogenic light chains at levels below the detection threshold of traditional serologic methods is hypothesized to impede organ response in some patients. Assessment of minimal residual disease (MRD) may therefore have clinical importance as a more stringent treatment response tool for patients in a hematologic complete response. We used 2-tube, 10-color combination multiparametric flow cytometry to assess for MRD at a minimum sensitivity of 1 in 105 nucleated cells. Of 65 patients in hematologic complete response, 36 (55%) were found to have a residual clonal plasma cell population in the bone marrow. Comparing the MRD-negative and MRD-positive groups, renal response was observed in 88% vs 64% (P = .06), cardiac response in 75% vs 59% (P = .45), and any organ response in 90% vs 75% (P = .20) of patients. Depth of organ response as measured by the percent decrease in 24-hour proteinuria and brain natriuretic peptide was 96% vs 91% (P = .16) and 55% vs 46% (P = .66), respectively. These data suggest a possible correlation between MRD negativity and higher probability of organ response after treatment in AL amyloidosis. Future prospective studies with a larger cohort are needed to determine the clinical relevance of these improvements. This trial was registered at www.clinicaltrials.gov as #NCT00898235.