Modified High-Dose versus High-Dose Melphalan Conditioning in Older Patients Undergoing Autologous Stem Cell Transplantation for Immunoglobulin Light Chain Amyloidosis.

High-dose melphalan and autologous stem cell transplantation (HDM/SCT) induces deep hematologic responses (HR) in patients with newly diagnosed systemic immunoglobulin light-chain (AL) amyloidosis. Modifying melphalan conditioning dose (mHDM <140 mg/m2) is considered in older patients because of concerns regarding tolerability. Age does not predict frailty, and dose modification could compromise responses in an era where effective non-transplant regimens are available. We analyzed 43 patients ≥ 65 years with AL amyloidosis who underwent SCT at Boston University Amyloidosis Center between 2011 and 2020. Median age was 66 years (range 65-68) versus 69 years (range 65-76) in the HDM and mHDM groups, respectively. HR of ≥ very good partial response at 12 months was 66.7% versus 42.3% for patients treated with HDM versus mHDM. Median progression-free survival (PFS) from day 0 of SCT was not reached versus 12.0 months (P =.13); grade ≥ 3 non-hematologic transplant-related toxicities occurred in 87.5% versus 76.9%; and transplant-related mortality was 0% versus 2.3% in the HDM versus mHDM group, respectively. In carefully selected older patients with AL amyloidosis, HDM is well tolerated. Use of mHDM results in reduced HR and PFS; an important consideration with the advent of highly effective non-transplant therapies.