DISCUSSION
Our study provides evidence pointing to inequity in outcome for
Aboriginal children and for children from remote and very remote
localities with acute leukaemia in Australia. There was no association
found between MRD-based response and either ethnicity or remoteness of
residence, suggesting the lower survival among Aboriginal children and
those from remote areas is independent of this measure.
It is widely known that cancer is more likely to be fatal in Indigenous
adults compared to non-Indigenous counterparts3. There
have been few studies performed in Indigenous children, particularly
within a specific cancer type. A study by Valery et al. revealed
a reduced 5-year survival of 75% for Indigenous children with any type
of cancer in Australia compared to 82.3% for non-Indigenous
children3. Furthermore, Indigenous children had 1.36
times greater risk of death within 5 years of diagnosis after
adjustments for rurality of residence, SES, cancer diagnosis and year of
diagnosis3,13.
Previous studies worldwide have shown higher overall cancer incidence
and mortality in minority ethnic groups, such as Maori and Pacific
Islander people in New Zealand (NZ)4,5. Black children
with acute leukaemia and those from other ethnic or racial minority
groups in the United States of America have inferior survival compared
to Caucasian children6-8. Measures have been taken to
address the inequalities in cancer outcome and incidence between Maori
and non-Maori people, such as introducing specific services for Maori
people4. Similar measures are required to address the
gap in survival rates for Aboriginal children with leukaemia in
Australia.
It has been estimated that 76% of Indigenous children under 15 years of
age in NT reside in remote and very remote parts of Australia compared
to 13% in SA and 36% in WA14. However, data on
childhood cancer incidence by remoteness of residence and SES are
scarce15. Consistent with previous
studies2, our study has shown Aboriginal children were
less likely to live in major cities. Applying the ARIA remoteness index,
this showed that Aboriginal children were more likely to live in
communities further away from medical centres (Table 1). Furthermore, no
Aboriginal children in our study lived in the least disadvantaged areas.
Whilst these numbers were small, this trend warrants further research.
A study by Youlden et al. revealed that children living in more
urban areas in Australia had higher cancer rates overall, particularly
for leukaemia and lymphoma15. It was postulated that
the reduced incidence of childhood cancers in remote and very remote
areas could potentially be related to reduced incidence of cancer in
Indigenous residents or missed diagnosis due to non-presentation. The
incidence rates of childhood cancer were slightly higher among children
in the least socioeconomically disadvantaged areas in Australia compared
to those in the most disadvantaged areas15. Whilst
this study did not yield population data for SA, NT and WA, analysing
rates of leukaemia between areas of remoteness and different SES should
be considered for future studies.
Worldwide, there has been inconclusive evidence that geographic
residence impacts on overall survival9 although
previous Australian studies have indicated poorer rates of survival for
children with cancer who live in more isolated parts9.
One would expect that with increasing remoteness comes reduced access to
healthcare and increased challenges associated with diagnosis, treatment
and long-term follow-up15. It is not known whether the
reduced survival in remote areas is due to the larger relative
percentage of Indigenous people9.
Generally, an inferior outcome has been observed in children with cancer
from lower or middle-income countries; however, results from low
socioeconomic demographics in high-income countries are less
consistent16. A study from Queensland in the early
1980s reported a significant difference in incidence and survival among
children with ALL across different SES, despite similar treatments being
received9,17. This trend was also observed in Maori
and Pacific people in NZ5. Further research is clearly
warranted to evaluate causes of poorer outcomes in children from remote
areas, lower socioeconomic advantage and from various ethnicities.
An overrepresentation of AML patients in Aboriginal children diagnosed
and treated in SA (WCH) between 1978 and 1998 was first reported in an
audit by Bartle et al. in 19991. These patients
were less likely to speak English and more likely to come from
traditional Aboriginal communities1. This was
confirmed 12 years later by Rotte et al. , who again found
relatively more cases of AML diagnosed among Aboriginal children at WCH
between 1997 and 20112. The latest cohort of patients
from the same geographical area (SA/NT) reported here has also shown a
higher proportion of AML cases and again without obvious morphological
phenotype or cytogenetic abnormality1. The
over-representation of AML in Aboriginal children in SA/NT observed in
three successive cohorts since 19781-2 warrants
further investigation and interestingly was not observed here in
Aboriginal children from WA. Our study also seems to indicate lower
overall survival of children with AML compared to current Australian
Childhood Cancer Statistics (69.8% vs. 77.6%)18,
although this may be because the latter only includes children diagnosed
before the age of 15 rather than 18.
Despite small patient numbers, there was a significant difference
observed in clinical trial enrolment and follow-up among Aboriginal
children. Previous studies have reported lower participation rates in
clinical trials2, which is likely to contribute to a
less optimal outcome given less rigorous adherence to diagnostic and
therapeutic guidelines2. Cultural and language
barriers can also make discussions regarding randomised trial and
informed consent challenging2.
Consistent with previous studies2, we found a lower
rate of follow-up among Aboriginal children, with a statistically
significant increase in those lost to follow-up. As discussed
previously, this may reflect inequality in healthcare access for those
in rural and remote communities. Improvements could be made by
expediting use of tele-conferencing to support a shared care model and
utilisation of rural outreach oncology nurses to enhance communication
with local healthcare workers2. Furthermore,
simplification of care, community involvement, peer support and
decentralisation of care may also improve service delivery for
Aboriginal and remote people19.
Strengths from this study are the high level of data quality obtained
from the contributing centres. Limitations include the relatively small
cohort size and subsequently small number of Aboriginal children
included, leading to reduced statistical power. Furthermore, given only
patients were included from SA, NT and WA, there is not complete
population coverage of data. This could potentially introduce bias,
however this risk is small given most children diagnosed with leukaemia
in these states/territories are referred to the major paediatric
oncology treating hospitals included in the study. Indigenous status was
defined by self-assessment at the involved centres and the accuracy of
these data is unknown. Nevertheless, any misclassification of Indigenous
status is likely to be random with respect to the factors examined here,
thus is unlikely to have biased our results.