Cancer incidence and survival among Métis adults in Canada: results from the Canadian census follow-up cohort (1992-2009).

BACKGROUND: Métis people are 1 of 3 Aboriginal groups recognized by the Canadian constitution. We estimated site-specific incidence rates and survival for the most common cancers among Métis adults in Canada and compared these with rates among non-Aboriginal adults in Canada. METHODS: We examined responses to the 1991 long-form census, including self-reported Métis ancestry linked to national mortality and cancer databases for followup from 1992 to 2009. We estimated age-standardized incidence rates and 5-year relative survival. We determined relative risk (RR) of cancer among Métis and non-Aboriginal adults using Poisson regression, and estimated excess mortality rate ratios using ethnicity-specific life tables. RESULTS: For all cancers and both sexes combined, cancer incidence was similar for Métis and non-Aboriginal adults. However, incidence was significantly higher among Métis adults than among non-Aboriginal adults for the following cancers: female breast (RR 1.18, 95% confidence interval [CI] 1.02-1.37), lung (RR 1.34, 95% CI 1.18-1.52), liver (RR 2.09, 95% CI 1.30-3.38), larynx (RR 1.60, 95% CI 1.03-2.48), gallbladder (RR 2.35, 95% CI 1.12-4.96) and cervix (RR 1.84, 95% CI 1.23-2.76). Métis people had poorer survival for prostate cancer (excess mortality rate ratio 2.60, 95% CI 1.52-4.46). INTERPRETATION: We found higher incidence for several cancers and poorer survival after prostate cancer among Métis adults. Several of these disparities may be related to lifestyle factors (including tobacco use, obesity and lack of cancer screening), providing evidence to support development of public health policy and health care to address cancer burden in the Métis people of Canada.

Choice of relative or cause-specific approach to cancer survival analysis impacts estimates differentially by cancer type, population, and application: evidence from a Canadian population-based cohort study.

BACKGROUND: Cause-specific (CS) and net survival in a relative survival framework (RS) are two of the most common methods for estimating cancer survival. In this paper, we assess the differences in results produced by two permutations of cause-specific and relative survival applied to estimating cancer survival and disparities in cancer survival, using data from First Nations and non-Aboriginal populations in Canada. METHODS: Subjects were members of the 1991 Canadian Census Mortality Cohort, a population-based cohort of adult respondents to the 1991 Long Form Census who have been followed up for incident cancers and death through linkage to administrative databases. We compared four methods: relative survival analyses with ethnicity-specific life tables (RS-ELT); relative survival with general population life tables (RS-GLT); cause-specific survival with a broad definition of cancer death (CS-Broad); and cause-specific survival with a narrow definition of cause of death (CS-Narrow) and applied these to the nine most common cancers among First Nations. RESULTS: Apart from breast and prostate cancers, RS-ELT, RS-GLT, and CS-Broad tended to produce similar estimates of age-standardized five-year survival, whereas CS-Narrow yielded higher estimates of survival. CS-Narrow estimates were particularly unlike those based on the other methods for cancers of the digestive and respiratory tracts. Estimates of disparities in survival were generally comparable across the four methods except for breast and prostate cancers. CONCLUSIONS: Cancer surveillance efforts in sub-populations defined by race, ethnicity, geography, socioeconomic status, or similar factors are necessary for identifying disparities and monitoring progress toward reducing them. In the absence of routine monitoring of cancer survival and cancer survival disparities in these populations, estimates generated by different methods will inevitably be compared over time and across populations. In this study, we demonstrate that caution should be exercised in making these comparisons, particularly in interpreting cause-specific survival rates with an unknown or narrow definition of cancer death and in estimates of breast and prostate cancer survival and/or disparities in survival generated by different methods.

Cancer Survival Disparities Between First Nation and Non-Aboriginal Adults in Canada: Follow-up of the 1991 Census Mortality Cohort.

BACKGROUND: The burden of cancer among indigenous people in Canada has been understudied due to a lack of ethnic identifiers in cancer registries. We compared cancer survival among First Nations to that among non-Aboriginal adults in Canada in the first national study of its kind to date. METHODS: A population-based cohort of approximately 2 million respondents to the 1991 Canadian Long Form Census was followed for cancer diagnoses and deaths using probabilistic linkage to cancer and death registries until 2009. Excess mortality rate ratios (EMRR) and 5-year age-standardized relative survival rates were calculated for 15 cancers using age, sex, ethnicity, and calendar-time-specific life tables derived from the cohort at large. RESULTS: First Nations diagnosed with cancers of the colon and rectum, lung and bronchus, breast, prostate, oral cavity and pharynx, cervix, ovary, or with non-Hodgkin lymphoma and leukemia all had significantly poorer 5-year survival than their non-Aboriginal peers. For colorectal cancer, a significant disparity was only present between 2001 and 2009 (EMRR: 1.52; 95% CI, 1.28-1.80). For prostate cancer, a significant disparity was only present between 1992 and 2000 (EMRR: 2.76; 95% CI, 1.81-4.21). Adjusting for income and rurality had little impact on the EMRRs. CONCLUSIONS: Compared with non-Aboriginals, First Nations people had poorer survival for 14 of 15 of the most common cancers, and disparities could not be explained by income and rurality. IMPACT: The results of this study can serve as a benchmark for monitoring progress toward narrowing the gap in survival. Cancer Epidemiol Biomarkers Prev; 26(1); 145-51. ©2016 AACR.

Colorectal cancer incidence in the Aboriginal population of Ontario, 1998 to 2009.

BACKGROUND: Studies suggest that colorectal cancer incidence increased disproportionately among the Aboriginal population of Ontario relative to the general population. Using an ecological approach, this study examined colorectal cancer incidence for the 1998-to-2009 period among Aboriginal people living in Ontario. DATA AND METHODS: Based on their postal code when they were diagnosed, cases of colorectal cancer identified from the Ontario Cancer Registry were assigned to census geographic areas with high (33% or more) or low percentages of Aboriginal identity residents, using the Postal Code Conversion File Plus (PCCF+). To account for potential misclassification by the PCCF+, Indian reserves for which assignment through postal codes is likely to be accurate were identified. Age-standardized incidence rates and rate ratios were calculated to compare colorectal cancer incidence in high-Aboriginal identity areas or on Indian reserves with incidence in low-Aboriginal identity areas. RESULTS: Colorectal cancer incidence was significantly higher for residents of high- versus low-Aboriginal identity areas in Ontario (rate ratio for men = 1.44, 95% CI = 1.26-1.63; rate ratio for women = 1.42, 95% CI = 1.23-1.63), a disparity that persisted by age group. When the Aboriginal sample was limited to residents of Indian reserves, the difference was statistically significant only for men and for people aged 50 to 74. INTERPRETATION: The incidence of colorectal cancer differs across areas of Ontario with high and low percentages of Aboriginal identity residents.

Cancer survival among First Nations people of Ontario, Canada (1968-2007).

We aimed to compare cancer survival in Ontario First Nations people to that in other Ontarians for five major cancer types: colorectal, lung, cervix, breast and prostate. A list of registered or "Status" Indians in Ontario was used to create a cohort of over 140,000 Ontario First Nations people. Cancers diagnosed in cohort members between 1968 and 2001 were identified from the Ontario Cancer Registry, with follow-up for death until December 31st, 2007. Flexible parametric modeling of the hazard function was used to compare the survival experience of the cohort to that of other Ontarians. We considered changes in survival from the first half of the time period (1968-1991) to the second half (1992-2001). For other Ontarians, survival had improved over time for every cancer site. For the First Nations cohort, survival improved only for breast and prostate cancers; it either declined or remained unchanged for the other cancers. For cancers diagnosed in 1992 or later, all-cause and cause-specific survival was significantly poorer for First Nations people diagnosed with breast, prostate, cervical, colorectal (male and female) and male lung cancers as compared to their non-First Nations peers. For female lung cancer, First Nations women appeared to have poorer survival; however, the result was not statistically significant. Ontario's First Nations population experiences poorer cancer survival when compared to other Ontarians and strategies to reduce these inequalities must be developed and implemented.

Stage at diagnosis and comorbidity influence breast cancer survival in First Nations women in Ontario, Canada.

BACKGROUND: Indigenous populations in Canada and abroad have poorer survival after a breast cancer diagnosis compared with their geographic counterparts; however, the influence of many demographic, personal, tumor, and treatment factors has not been examined to describe this disparity according to stage at diagnosis. METHODS: A case-case design was employed to compare First Nations (FN) women (n = 287) to a frequency-matched random sample of non-FN women (n = 671) diagnosed with breast cancer within the Ontario Cancer Registry. Women were matched on period of diagnosis (1995-1999 and 2000-2004), age at diagnosis (<50 vs. ≥50), and Regional Cancer Centre (RCC). Stage and other factors were collected from medical charts at the RCCs. Survival was compared using an adjusted Cox proportional hazards model and stratified by stage at diagnosis (I, II, and III-IV). Determinants of survival in FN women stratified by stage at diagnosis were also modeled. RESULTS: Survival was more than three times poorer for FN women diagnosed at stage I than for non-FN women (HR = 3.10, 95% CI = 1.39-6.88). The risk of death after a stage I breast cancer diagnosis was about five times higher among FN women with a comorbidity other than diabetes (HR = 4.65, 95% CI = 1.39-15.53) and was more than five times greater for women with diabetes (HR = 5.49, 95% CI = 1.69-17.90) than for those without a comorbidity. CONCLUSIONS: Having a preexisting comorbidity was the most important factor in explaining the observed survival disparity among FN women. IMPACT: Improving the general health status of FN women could increase their survival after an early-stage breast cancer diagnosis.

Detection of later stage breast cancer in First Nations women in Ontario, Canada.

OBJECTIVE: To compare the distribution of stage at breast cancer diagnosis between First Nations (FN) and non-FN women, and to investigate factors associated with later diagnosis in FN women. METHODS: A case-case design was employed to compare FN women (N = 287) to a frequency-matched random sample of women (N = 671) from the general population diagnosed with breast cancer in the Ontario Cancer Registry. Women were matched (2:1) on period of diagnosis (1995-1999, 2000-2004), age at diagnosis (< 50 vs. > or = 50), and Regional Cancer Centre (RCC). Stage and data relevant to the determinants of stage were collected from medical charts at the RCCs. The association between stage (stage II + vs. I) and FN status was modeled using logistic regression analyses; for FN women, the association between risk factors and stage was examined. RESULTS: FN women (66%) were diagnosed with a later stage significantly more often than non-FN women (56%). FN women with a non-screened cancer (OR 5.03, 95% CI 2.48-10.21) and those who were overweight or obese (OR 2.98, 95% CI 1.27-6.98 and OR 4.46, 95% CI 1.95-10.21, respectively) were significantly more likely to be diagnosed at a later stage. Having a comorbidity reduced the odds of a later stage (OR 0.51, 95% CI 0.27-0.96) in FN women. CONCLUSION: This study demonstrates the need for FN women, in particular those who are not accessing the health care system, to participate in breast screening programs aimed at detecting breast cancers earlier with a better prognosis. These findings suggest that the cancer care system in Ontario should better target this population through increasing awareness and access to screening.