Impact of Hematopoietic Cell Transplantation Comorbidity Index (HCT-CI) on AL Amyloidosis Outcomes

Background Autologous stem cell transplantation (ASCT) remains the preferred standard consolidation therapy for patients with AL amyloidosis. Whilst several factors are known to impact outcomes, conventional risk scores for transplant-related mortality such as the HCT-CI have not been fully explored in this setting. Objectives To compare progression-free survival (PFS) and overall survival (OS) by HCT-CI status for AL patients who underwent ASCT. Methods All consecutive patients with AL amyloidosis who underwent ASCT using single agent melphalan conditioning regimen were included. Primary endpoints were PFS and OS. Secondary endpoints included cumulative incidence of relapse (CIR) and non-relapse mortality (NRM) rates. Hematologic response was defined per the 2012 consensus criteria. Survival estimates were calculated using Kaplan-Meier method. Results One-hundred-and-seventy-nine patients, with a median age of 61 (range, 27-77) years, were identified between 09/2005 and 11/2021, of which 108 (60%) had low HCT-CI ≤3 and 71 (40%) had HCT-CI >3. Table 1 summarizes patient and disease characteristics for all study patients and by HCT-CI. With a median follow up of 62 months (range 3.2-167.4), the 5-year PFS and OS for all study patients were 49% and 72%, respectively. The 5-year PFS/OS rates for HCT-CI ≥3 were 46%/65% compared to 51%/76% for HCT-CI<3 (p=0.05056 for PFS; p=0.0393 for OS). Multivariable analyses included HCT-CI and factors with p value ≤0.1 in the UVA for PFS (age, Revised Mayo Staging, and dFLC) and OS (Age, eGFR, and Revised Mayo Staging). In MVA, none of the factors had statistically significant impact on PFS. Age ≥60 (HR 2.32, 95% CI: 1.13-4.78; p=0.0221) and Revised Mayo Stage III/IV (HR 2.76, 95% CI: 1.37-5.4; p=0.0042) were significantly associated with inferior OS, with a trend for inferior outcome with HCT-CI ≥3 (HR 1.84, 95% CI: 0.93-3.67; p=0.0815). There was no significant difference in 5-year CIR (39% for HCT-CI ≤3 vs 35% for HCT-CI >3; p=0.4305). HCT-CI >3 was associated with a higher 5-year NRM of 19% compared to 11% for patients with HCT-CI≤3 (p=0.0530). In a subgroup analysis stratifying patients by their age and HCT-CI, patients ≥60 years with a higher HCT-CI had significantly inferior 5-year OS/NRM of 52%/25% (p=0.0013 for OS; P=0.0376 for NRM). (Figure). Conclusion For AL amyloidosis patients who underwent ASCT, age ≥60 and Revised Mayo stage III/IV are strong predictors for inferior survival. The HCT-CI score is a valuable adjunct in predicting NRM and OS in patients undergoing ASCT for AL amyloidosis, particularly those older than 60 years. HCT-CI may be used to predict an ultra-high-risk group, for whom alternative treatment approaches may be warranted. Larger studies are needed to validate these findings.