Abstract
AL amyloidosis is caused by a clonal plasma cell dyscrasia and characterized by widespread, progressive deposition of amyloid fibrils derived from monoclonal Ig light chains, leading to multisystem organ failure and death. Aggressive treatment of AL amyloidosis with high-dose melphalan followed by autologous stem cell transplant (HDM/SCT) can induce hematologic and clinical remissions and extend survival. Several approaches have been used to define hematologic responses following HDM/SCT and other forms of treatment. The standard definition of a hematologic complete response (CR) that we have used requires that there be no evidence of a persistent monoclonal gammopathy by immunofixation electrophoresis (IFE) of serum and urine proteins, or of a persistent plasmacytosis or plasma cell clonality in a bone marrow biopsy by immunohistochemistry. Others have defined hematologic responses according to reductions in free light chain (FLC) measurements. Treatment responses as defined by both criteria correlate with survival and clinical improvement following HDM/SCT. We have carried out a prospective analysis of HDM/SCT treatment outcomes for patients with AL amyloidosis to determine the extent to which early FLC responses within weeks of treatment predict hematologic CR, as defined by our standard criteria. Serum free light chain concentrations (FLC) were measured by a sensitive nephelometric immunoassay in 31 patients with AL amyloidosis, between 2003–2005, 1–3 weeks after treatment with HDM/SCT. Hematologic responses, as defined by standard criteria, as well as FLC responses were subsequently determined at 3, 6 and 12 months. Serum FLC levels or κ/λ FLC ratios were abnormal and informative in 28 patients (90%) prior to HDM/SCT, and these patients were included in subsequent analyses. Twenty patients (71%) achieved normalization of abnormal serum FLC levels or ratios within 1–3 weeks of undergoing HDM/SCT. Of these 20 patients, 13 patients (65%) subsequently achieved a hematologic CR as defined by standard criteria, while 7 (35%) did not, within 3 months following HDM/SCT. In contrast, none of the 8 patients with no demonstrable FLC response within 1–3 weeks of HDM/SCT, were found to have achieved a hematologic CR subsequently. In conclusion, meaningful quantitative FLC responses (or lack of response) can be detected within weeks following HDM/SCT treatment that predict hematologic responses, as defined subsequently by standard criteria based on IFE and marrow studies (p=0.0018 by chi square analysis). Moreover, a lack of an early FLC response predicts for hematologic non-CR. We anticipate that prospective studies of FLC responses in HDM/SCT and other clinical trials for AL amyloidosis will eventually lead to more rapid assessment of treatment responses that will guide therapeutic decisions.
Author notes
Corresponding author
