Delineation of the timing of second-line therapy post-autologous stem cell transplant in patients with AL amyloidosis.

Among patients with immunoglobulin light chain (AL) amyloidosis, there is little consensus on when reinstitution of chemotherapy should occur. We conducted a retrospective study to evaluate the patterns of relapse or progression (R/P) and the timing of reinitiating therapy among 235 patients initially treated with autologous stem cell transplant (ASCT) at Mayo Clinic. The median time from ASCT to second-line therapy was 24.3 months. At the time of restarting therapy, median difference of free light chain (dFLC) was 9.9 mg/dL (42% of diagnosis value), 32% had a dFLC <5 mg/dL, and 63% met criteria for organ R/P. The indications for retreatment were (1) clinical suspicion of R/P, 10%; 92) hematologic R/P only, 23%; (3) organ R/P only, 32%; (4) both hematologic and organ R/P, 31%; and (5) suboptimal response to ASCT and second-line therapy as consolidation, 4%. Patients with organ progression at the time of second-line therapy had inferior survival. Although a dFLC of >5 mg/dL at the time of reinstituting therapy was associated with risk, patients relapsing from very good partial response (VGPR) or better had a longer time to develop organ progression after hematologic R/P (24.2 vs 3.2 months, P = .007). These data suggest that the best candidates for clinical trials testing novel plasma cell-directed chemotherapy beyond first line may be those patients who are either relapsing from VGPR or better (dFLC at diagnosis was >5 mg/dL) or having inadequate response to prior therapy. This strategy should allow for hematologic response assessment while avoiding the risk of deleterious organ progression. Implementation of more stringent progression criteria may also be warranted.