Discussion
Older studies, well summarized by Majhail et al indicate racial
disparities associated with access to HCT as well as outcomes after HCT
(11). Analyses of data from 1988-2002 including hospital discharge data,
CIBMTR, SEER and US Census bureau data indicated that when compared to
W, adult B patients were less likely to receive HCT for hematologic
malignancies. (12,13) However, these differences in access to HCT were
not present in younger patients. (12,14) All patients in our study
received HCT and thus had access to this tertiary center, high-cost
care. We did not have data that would allow evaluation of access to
transplant by race. Indirect evidence, such as racial distribution of
our patients (75% W, 18% B and 3% Asians), which correlated well with
overall Florida population (2018 US Census Bureau estimates) comprising
75% W (53% Non-Hispanic White), 16% B and 2.8 % Asians, and time
from diagnosis to transplant, which was actually 3 months shorter in B
than W children, suggests that access to transplant was not an issue.
However, B and W HCT recipients do not have the same access to
HLA-matched donors. Increased diversity in HLA haplotypes among B
populations, and underrepresentation of minorities in national bone
marrow registries contribute to difficulty in finding fully matched
unrelated donors for B patients and other minority HCT-recipients.
(4,15) Only 16 B children (29%) in our study received a fully
HLA-matched HCT during this 10-year period.
The largest study describing the effects of race and socioeconomic
status on outcomes of unrelated donor HCT (1995-2004), which included
~1600 children <20 years, did not
differentiate outcomes based on age. (7) When adult and pediatric
populations were analyzed together, Baker et al showed that
African-Americans but not Asian or Hispanic HCT recipients of unrelated
donor transplants had significantly worse overall survival than W.
African-Americans as well as Hispanics had higher treatment-related
mortality than W. Also, patients with median income in the lowest
quartile across racial groups, had worse OS and higher risk of treatment
related mortality (7). Our study indicated that the majority of B
patients (71%) and 53% of W patients received an
HLA-mismatched/alternative donor HCT. This is similar to Baker’s study
where 78% of B and 54% W received an HCT from a MMUD (7). Despite a
larger proportion of HLA-mismatched transplants among B children in our
study, overall survival and other outcomes were not different between W
and B HCT recipients. In addition, unlike W, who had a significantly
lower survival after HLA-mismatched HCT, which is well described in the
literature, B HCT recipients had identical outcomes after HLA-matched
and HLA-mismatched transplants. Only 16 B patients received a fully-HLA
matched transplant over a 10 year period and survival rates in this
group were likely skewed due to low patient numbers. Although more B
than W patients received HLA-mismatched HCT, they were more likely to
receive MMRD, than MMUD BM or PB. Black children receiving
MMRD/haploidentical transplant had a 2-year survival rate of 70%,that
did not subsequently decline. Although we do not have details of GVHD
prophylaxis for patients receiving alternative donor transplants, all 5
FPBCC centers utilize post-transplant cyclophosphamide (PTCy), while
only one center has the access to in vitro T-cell depletion. Recent
reports indicate improved outcomes of recipients of haplo-identical HCT
using PTCY for GVHD prophylaxis. (16) Similar to our findings, a recent
randomized study indicated improved overall survival in haploidentical
HCT recipients with PTCY comparing with recipients of MMUCB transplant.
(17) Although deaths due to relapse and treatment-related causes were
not different between W and B HCT-recipients, we noticed an unacceptably
high rate of death (22-25%) due to treatment-related causes. Lowering
those rates for all children will be one of the FPBCC priorities.
Despite limitations of our study including relatively small number of
patient, lack of data on socio-economic status, ethnic origin, and lack
of detailed data on GVHD prophylaxis, this is the largest contemporary
pediatric study examining outcomes by race in children with HM
undergoing HCT. Overall, our results are encouraging as they show that
lack of HLA-matched donors did not translate into adverse HCT outcomes
for B children.