Interpretation
These findings reinforce information available from other contexts.
Population studies from the US have consistently shown that socially and
financially disadvantaged endometrial cancer patients have more limited
prognosis. Two large studies using the National Cancer Database (NCDB)
to evaluate endometrial cancer patients found that Black race, insurance
status, lower income and education were all independently associated
with increased mortality 18,20. Similarly, a
Surveillance, Epidemiology and End Results (SEER) cancer database study
evaluating a large endometrial cancer cohort with long term follow up26 reported higher overall and cancer-specific
mortality among Black patients, and tied this to disparities in
presentation and treatment. However, publications from the US may not be
transferrable to the Canadian context, due to the complexity of the
American healthcare payer system and financially-driven barriers to
access.
American data on the association between SDH and endometrial cancer
outcomes focuses heavily on racial marginalization13,18,20,24,26,27. Race differs from ethnicity6 and is not routinely collected in Canadian
administrative and healthcare databases. Our findings did not support an
association between ethnic marginalization and overall survival in
Ontarian women with endometrial cancer. The ethnic concentration domain
of the Canadian Marginalization Index reflects the concentration of
self-identified ethnic minorities and new immigrants in the community35. We postulate that the healthy immigrant effect may
partially counterbalance the effects of social, cultural and financial
marginalization often associated with ethnic concentration36. In support of this, a targeted analysis of
immigration status in our patient population found that recent
immigration to Canada is, in fact, associated with improved overall
survival (HR=0.58 for new residents within 5 years, p=0.002).
Data from other jurisdictions with public healthcare systems are also
consistent with our findings in Ontario: Population-based studies from
Sweden 17 and from the UK 16 have
described higher rates of advanced-stage endometrial cancer among
socially disadvantaged women; however, disease outcomes were not
compared in these studies. Cooper et al report data from national
statistics, including over 53,000 endometrial cancer patients, in
England and South Wales 37 between 1986-1999; they
note a deprivation gap in endometrial cancer survival which has not
narrowed over the 15-year study period. Finally, a comprehensive cancer
registry study from Australia 38 demonstrates a
significant excess risk of death in disadvantaged endometrial cancer
patients from communities with low levels of educational attainment and
skilled employment.
Disparities in cancer incidence and outcomes in marginalized populations
have been linked to adverse health behaviors 39, and
many publications on the association of SDH with cancer outcomes
evaluate diseases with behavioral risk factors, such as lung cancer,
head and neck tumors and cervical cancer rates7,40–42. We chose to focus on a neoplasm which is not
associated with smoking or with sexual behavior in an attempt to
mitigate confounders. However, obesity is a well-established risk factor
for endometrial cancer 43–46 and has consistently
been linked to social marginalization 47. We did not
have access to individual-level BMI, but were able to capture severe
obesity (BMI>40) through billing codes. We found that
severe obesity was inversely associated with the risk of death; this may
be explained by the fact that obesity increases the risk for
estrogen-dependent tumors 43–46, which are primarily
well-differentiated and carry a better prognosis. This hypothesis is
supported by the findings on multivariable analysis, where the
association between obesity and improved survival did not persist when
adjusted by disease histology and stage.