Optimizing Deep Response Assessment for AL Amyloidosis Using Involved Free Light Chain Level at End of Therapy
Authors: Muchtar Eli , Dispenzieri Angela , Leung Nelson , Buadi Francis K. , Dingli David , Hayman Suzanne R. , Kapoor Prashant , Hwa Yi L. , Fonder Amie , Hobbs Miriam , Gonsalves Wilson I , Kourelis Taxiarchis , Warsame Rahma , Russell Stephen J. , Lust John A. , Lin Yi , Go Ronald S. , Zeldenrust Steven , Kyle Robert A. , Rajkumar S. Vincent , Kumar Shaji K. , Gertz Morie A. 
Published: October 2019

Abstract
Introduction: Light chain burden in light chain (AL) amyloidosis is often low, making accurate response assessment challenging.
Methods: AL amyloidosis patients achieving very good partial or complete response to first line therapy and had serial sFLC studies during and after completion of therapy were included (n=396). Involved free light chain (iFLC), difference in involved-to-uninvolved free light chains (dFLC) and sFLC ratio (sFLCR) were assessed at the end of first line therapy and at nadir iFLC. Survival analysis was done using the Kaplan-Meier method. Hematological progression-free survival (hemPFS) was defined as the time from diagnosis until hematological progression or death, where patients known to be alive and progression-free at the end of follow-up were censored. Hematological progression was defined according to consensus criteria or upon initiation of second line therapy, whichever came first.
Results: The median iFLC and dFLC at the end of therapy was 1.7 mg/dL and 0.5 mg/dL, respectively. sFLCR normalization occurred in 70% of patients. iFLC ≤2 mg/dL and dFLC ≤0.5 mg/dL were associated with a longer hemPFS compared to their counterparts (Figure). Only iFLC ≤2 mg/dL was associated with a significantly longer overall survival (Figure). sFLCR normalization did not predict hemPFS or overall survival. Organ response was predicted by iFLC ≤2 mg/dL and dFLC ≤0.5 mg/dL (Table), with best discrimination seen with iFLC ≤2 mg/dL. Organ response was not predicted by sFLC normalization (Table). The median nadir iFLC was 1.4 mg/dL and was reached 3.9 months from the end of therapy, longer in transplanted patients compared to patients treated with non-transplant regimens (7.3 vs 1.8 months, respectively; P<0.001). iFLC ≤2 mg/dL at the completion of therapy and nadir iFLC reached >12 months from the end of therapy were favorable predictors of hemPFS/OS in a multivariate analysis.
Conclusion: iFLC at the end of first line therapy better predicts for organ response and survival than dFLC among deep responders. Normalization of sFLCR does not predict for organ response or survival and should not be used as measure of therapeutic efficacy.
Figure. Figure.

Disclosures
Dispenzieri: Celgene, Takeda, Prothena, Jannsen, Pfizer, Alnylam, GSK: Research Funding. Dingli:Alexion Pharmaceuticals, Inc.: Other: Participates in the International PNH Registry (for Mayo Clinic, Rochester) for Alexion Pharmaceuticals, Inc.; Alexion Pharmaceuticals, Inc.: Other: Participates in the International PNH Registry (for Mayo Clinic, Rochester) for Alexion Pharmaceuticals, Inc.; Millennium Takeda: Research Funding; Millennium Takeda: Research Funding. Kapoor:Celgene: Research Funding; Takeda: Research Funding. Russell:Vyriad: Equity Ownership. Kumar:Janssen: Membership on an entity's Board of Directors or advisory committees, Research Funding; KITE: Membership on an entity's Board of Directors or advisory committees, Research Funding; Celgene: Membership on an entity's Board of Directors or advisory committees, Research Funding; AbbVie: Membership on an entity's Board of Directors or advisory committees, Research Funding. Gertz:Alnylam: Honoraria; celgene: Consultancy; Ionis: Honoraria; Abbvie: Consultancy; annexon: Consultancy; janssen: Consultancy; spectrum: Consultancy, Honoraria; Research to Practice: Consultancy; Medscape: Consultancy; Apellis: Consultancy; Teva: Consultancy; Amgen: Consultancy; Prothena: Honoraria; Physicians Education Resource: Consultancy.