Abstract
BackgroundCancer makes up a large and increasing proportion of excess mortality for indigenous, marginalised and socioeconomically deprived populations, and much of this inequality is preventable. This study aimed to determine which cancers give rise to changing ethnic inequalities over time.MethodsNew Zealand census data from 1981, 1986, 1991, 1996, 2001, and 2006, were all probabilistically linked to three to five subsequent years of mortality (68 million person-years) and cancer registrations (87 million person years) and weighted for linkage bias. Age-standardised rate differences (SRDs) for Māori (indigenous) and Pacific peoples, each compared to European/Other, were decomposed by cancer type.ResultsThe absolute size and percentage of the cancer contribution to excess mortality increased from 1981–86 to 2006–11 in Māori males (SRD 72.5 to 102.0 per 100,000) and females (SRD 72.2 to 109.4), and Pacific females (SRD −9.8 to 42.2) each compared to European/Other.Specifically, excess mortality (SRDs) increased for breast cancer in Māori females (linear trend p < 0.01) and prostate (p < 0.01) and colorectal cancers (p < 0.01) in Māori males. The incidence gap (SRDs) increased for breast (Māori and Pacific females p < 0.01), endometrial (Pacific females p < 0.01) and liver cancers (Māori males p = 0.04), and for cervical cancer it decreased (Māori females p = 0.03). The colorectal cancer incidence gap which formerly favoured Māori, decreased for Māori males and females (p < 0.01).The greatest contributors to absolute inequalities (SRDs) in mortality in 2006–11 were lung cancer (Māori males 50 %, Māori females 44 %, Pacific males 81 %), breast cancer (Māori females 18 %, Pacific females 23 %) and stomach cancers (Māori males 9 %, Pacific males 16 %, Pacific females 20 %). The top contributors to the ethnic gap in cancer incidence were lung, breast, stomach, endometrial and liver cancer.ConclusionsA transition is occurring in what diseases contribute to inequalities. The increasing excess incidence and mortality rates in several obesity- and health care access-related cancers provide a sentinel warning of the emerging drivers of ethnic inequalities. Action to further address inequalities in cancer burden needs to be multi-pronged with attention to enhanced control of tobacco, obesity, and carcinogenic infectious agents, and focus on addressing access to effective screening and quality health care.Electronic supplementary materialThe online version of this article (doi:10.1186/s12885-016-2781-4) contains supplementary material, which is available to authorized users.
Highlights
Cancer makes up a large and increasing proportion of excess mortality for indigenous, marginalised and socioeconomically deprived populations, and much of this inequality is preventable
Ethnic inequalities in cancer mortality All-cause mortality declined for all ethnic groups across all six cohorts from 1981–84 to 2006–11
This study found that inequalities in cancer mortality increased in Māori males and females, Pacific females and possibly in Pacific males each compared to European/ Other
Summary
Cancer makes up a large and increasing proportion of excess mortality for indigenous, marginalised and socioeconomically deprived populations, and much of this inequality is preventable. This study aimed to determine which cancers give rise to changing ethnic inequalities over time. Changes in risk factor prevalence and cancer detection and treatment have been associated with declines in cancer mortality rates in many countries, not all ethnic groups have benefited . Several studies document the extent of ethnic and indigenous inequalities in cancer incidence and mortality [5, 6] and explore trends in inequalities over time [7, 8]. Much of the excess cancer incidence and mortality observed in indigenous and ethnic minority groups is due to causes associated with poverty and social exclusion, tobacco smoking, chronic infections, obesity and lower screening coverage [4]. The relative importance of these more proximal causes of cancer change over time, potentially requiring changes in the emphasis of policies aimed at addressing inequities in cancer outcomes
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