Take-aways:
- Although allogeneic HSCT has increased more than autologous in recent years, the latter remains the predominant type.
- The most common indications for autologous and allogeneic HSCTs were lymphoproliferative diseases and leukemias, respectively.
- HSCTs from related donors became more frequent than unrelated HSCTs starting in 2014.
Since 2006, hematopoietic stem cell transplantations (HSCTs) have jumped 76%, closing the gap in access to the therapy worldwide, according to a report published in the journal Haematologica. The survey also found that allogeneic HSCT procedures outpaced autologous ones globally.
The survey, led by Dietger Niederwieser, MD, PhD, of the University of Leipzig in Germany, assessed regional and global access to HSCTs and the challenges that remain with this treatment option.
“HSCT [procedures] are increasing steadily worldwide with narrowing gaps between regions and greater increase in allogeneic compared to autologous activity,” the authors wrote.
Survey Design
The retrospective, observational survey, conducted by the Worldwide Network of Blood and Marrow Transplantation (WBMT), included 1,662 HSCT teams in 86 countries. The survey focused only on patients treated for the first time with HSCT.
Data were submitted to the WBMT’s central reporting system between 2006 and 2016 and included detailed and validated information such as the main indication, stage of the disease, stem cell source, and allogeneic donor type (family matched, family mismatched, or unrelated).
Data prior to 2006 were taken from paper records of bone marrow transplants reported in the scientific literature or from member organizations that carried out early transplants.
Frequency of HSCTs Worldwide
The study documented a total of 1,298,897 HSCTs (57.1% autologous) from 1957 to 2016. The cumulative number of HSCTs reached a milestone of 500,000 in 2005 and then doubled to 1 million in 2012. Using post-2016 WBMT data that had not yet been validated, the authors projected a cumulative total of 1.5 million HSCTs worldwide by 2019.
Looking just at the validated WBMT data from 2006 to 2016, the survey identified a total of 697,934 procedures (54% autologous), with a yearly growth rate of 5.9% since 2006.
Despite the continuous increase in HSCTs, the number of HSCT teams performing the procedures roughly plateaued starting in 2012, reflecting increased activity per HSCT team, rising from 35.1 HSCTs per team in 2006 to 49.8 in 2016.
Examining data for 2016 regionally, of the 82,718 HSCTs reported that year, the majority were performed in Europe (45.2%) and North America (24.4%), followed by Asia (22.7%), Latin America (5.1%), and Africa/East Mediterranean (2.7%).
Most Frequent Indications
The most frequent indications were lymphoproliferative disorders (LPD; n=370,884, of which 88.4% were autologous) and leukemia (n=248,860, of which 94.9% were allogeneic).
Looking specifically at allogeneic HSCTs in 2016, the most common indication was leukemia (n=28,719), with the most frequent single indication being acute myeloid leukemia (n=14,334), followed by acute lymphoblastic leukemia (n=6,895), myelodysplastic syndromes/myeloproliferative neoplasms (n=5,616), and chronic myeloid leukemia (n=1,108).
The second most common indication for allogeneic HSCT was non-malignant disorders (n=5,427), which includes the subgroups bone marrow failure (49.5%), hemoglobinopathies (23.3%), and immunodeficiencies (17.9%). This was followed by LPD (n=3,972), of which 81.7% were Hodgkin disease (HD)/non-Hodgkin lymphoma (NHL) and 16.6% plasma cell disorders.
Looking specifically at autologous HSCTs in 2016, the most common indication was LPD (n=39,878; 84.2% of all autologous HSCTs). Within the LPD category, the most frequent single indications were plasma cell disorders (59.4%) and HD/NHL (40.4%).
Other Findings
Among the trends identified in the survey was a decrease in the number of autologous HSCTs worldwide for all leukemias (–51.1%). Outside of leukemia, however, the number of autologous HSCTs increased across almost all indications and regions, especially for LPD and non-malignant disorders.
Another trend was the increasing prevalence of related versus unrelated donors. Overall, related HSCTs become more common than unrelated HSCTs starting in 2014. The increase in related HSCTs was mainly due to the increasing use of non-identical related donors (39.5% of related HSCTs), which increased significantly over the last four years.
In terms of stem cell source, by 2016, peripheral blood became the predominant graft source in both autologous (99.7%) and allogeneic (72.8%) HSCTs. The use of cord blood as a source declined, accounting for just 13.9% of all unrelated and 6.7% of all allogeneic HSCTs in 2016. Bone marrow accounted for 20% of allogeneic HSCTs in 2016.
“While related HSCT is rising, largely due to increase in haploidentical HSCT, unrelated HSCT is plateauing and cord blood HSCT is in decline,” the authors wrote.
Equitable Access
Despite increasing use of allogeneic HSCT and its international expansion of access, the authors cautioned that “allogeneic HSCT is still associated with significant morbidity and mortality and remains an example of highly specialized, high-cost medicine.” However, over the last two decades, “allogeneic HSCT has undergone a constant technological evolution, with decreasing transplant-related morbidity and mortality and expansion of the donor pool.”
Addressing the challenge of equitable access to HSCT across the globe, the authors suggested that the best solution is to increase the HSCT activity per HSCT team. They noted that in developing countries, 50 HSCTs per team is considered reasonable, whereas the United States currently performs almost 100 HSCTs per team.
The study is limited by the reporting lag of the analysis. In addition, information on utilization of HSCT for specific illnesses and information on second or third HSCT are not currently available.
“The achievements obtained in the last decade should be an incentive to continue and even increase the common efforts to improve access and close the gap worldwide faster,” the authors concluded.
Reference
Niederwieser D, Baldomero H, Bazuaye N, et al. One and a half million hematopoietic stem cell transplants: continuous and differential improvement in worldwide access with the use of non-identical family donors. Haematologica. 2022;107(5):1045-1053.
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