Prognostic Significance of Stringent Complete Response after Stem Cell Transplantation in Immunoglobulin Light Chain Amyloidosis

Hematologic response has emerged as a powerful prognostic factor for survival in patients with immunoglobulin light chain (AL) amyloidosis. Patients achieving a complete response (CR), based on serum and urine analysis, survive longest. However, data regarding the impact of bone marrow features post-therapy on response and survival are limited. We evaluated the impact of achieving a stringent CR (sCR), defined as undetectable bone marrow clonal plasma cells by flow cytometry, in patients with AL amyloidosis receiving an autologous stem cell transplant. A total of 573 consecutive patients transplanted for AL amyloidosis at the Mayo Clinic between April 2002 and August 2016 were included in the analysis. Of 540 patients in whom response was assessable, 220 patients (41%) achieved a CR, of whom 212 (96%) had a bone marrow biopsy at time of response assessment and were further analyzed for determination of sCR; 166 patients (78%) with a CR achieved an sCR, representing 31% of the whole cohort. Patients achieving a CR had a higher median percentage of bone marrow plasma cells (10% for CR versus 6% for sCR, P = .03), more patients with bone marrow plasma cells ≥ 10% (50% for CR versus 33% for sCR, P = .04), and were less likely to receive chemotherapy before transplantation (30% for CR versus 49% for sCR, P = .03) compared with those achieving sCR. Median overall survival for all patients achieving a CR was 175 months and was not statistically different between those achieving an sCR compared with those achieving a CR only (median not reached for sCR versus 175 months for CR, P = .65). Progression-free survival, however, was significantly shorter in patients failing to achieve an sCR (151 months for sCR versus 72 months for CR, P = .0003). Bone marrow examination post-transplant in AL amyloidosis is important and identifies patients who fail to achieve an sCR and progress earlier.