Assessing outcomes following hematopoietic cell transplantation (HCT) poses challenges due to the necessity for systematic and often prolonged patient follow-up. Linking the HCT database of the Center for International Blood and Marrow Transplant Research (CIBMTR) with cancer registry data may improve long-term outcome ascertainment, but the reliability of mortality data in death certificates from cancer registries among HCT recipients remains unknown.
We compared the classification of vital status and primary cause of death (COD), as well as the length of follow-up between the CIBMTR and California Cancer Registry (CCR) to assess the feasibility of supplementing the CIBMTR with cancer registry data.
This retrospective study leveraged a linked CIBMTR-CCR dataset. We included patients who were California residents at the time of HCT and received a first allogeneic (alloHCT) or autologous (autoHCT) HCT for a hematologic malignancy diagnosed during 1991-2016. Follow-up was through 2018.
We analyzed 18,450 patients (alloHCT, n=8,232; autoHCT, n=10,218). Vital status agreement was 97.7% for alloHCT and 97.2% for autoHCT. Unknown COD was higher in CIBMTR (12.9%) than CCR (1.6%). After excluding patients with unknown COD information, the overall agreement of primary COD (cancer vs. noncancer) was 53.7% for alloHCT and 83.2% for autoHCT. This agreement was lower within the first 100 days following HCT (alloHCT=31.0%, autoHCT=54.6%). Compared with CIBMTR, deaths due to cancer were higher in CCR (alloHCT=90.0%, autoHCT=90.1% vs. alloHCT=47.3%, autoHCT=82.5% in CIBMTR). CIBMTR reports more frequently noncancer-related deaths, including graft-versus-host disease and infections. Cumulative incidence of cancer-specific mortality at 20 years differed particularly for alloHCT (CCR=53.7%, CIBMTR=27.6%). Median follow-up among alive patients was longer in CCR (alloHCT=6.0, autoHCT=4.7 years) than in CIBMTR (alloHCT=5.0, autoHCT=3.8 years).
Our findings highlight the completeness of vital status data in CIBMTR but reveal substantial disagreement in primary COD. Consequently, caution is required when interpreting HCT studies that only use death certificates to estimate cause-specific mortality outcomes. Improving the accuracy of COD registration and follow-up completeness by developing communication pathways between cancer registries and hospital-based cohorts may enhance our understanding of late effects and long-term outcomes among HCT survivors.
Copyright © 2023. Published by Elsevier Inc.
