Highlights
- A study has found that the 5-year breast cancer survival rate was worse among Ontario First Nations women with pre-existing diabetes than among First Nations women without pre-existing diabetes.
- To our knowledge, this is the first study in Ontario or elsewhere in Canada to show this survival discrepancy.
- Cancer care teams need to be aware of the potential impact of diabetes on breast cancer survival because breast cancer rates are increasing among First Nations women in Ontario and a high proportion of them have been diagnosed with diabetes.
An Ontario study found that First Nations women with diabetes who are diagnosed with breast cancer are at a twofold increased risk of dying within 5 years, compared to other First Nations women without pre-existing diabetes.[1] To investigate the influence of pre-existing diabetes on survival, the study linked provincial mortality data to a comprehensive dataset containing prognostic characteristics, such as stage at diagnosis.[2]
Of the 282 Ontario First Nations women diagnosed with breast cancer who were eligible for this study from 1995 to 2004, 67 (24%) were diagnosed with diabetes. After 5 years of observation, the overall survival rate among First Nations women with diabetes was 59.8%, compared with 78.7% among First Nations women without diabetes (p<0.01). Survival time was calculated for each woman, beginning at her date of breast cancer diagnosis until the date of death or at the end of the study, whichever occurred first.
Previous research has found that breast cancer prognosis in First Nations women in Ontario is worse than in non-First Nations women because when they are diagnosed with breast cancer,[3] they are more likely to:
- be diagnosed at a later stage of breast cancer
- have ever smoked
- have a higher body mass index
- have comorbidities (other conditions).
Studies of other populations have evaluated the association between pre-existing diabetes and survival after a breast cancer diagnosis. A meta-analysis showed that diabetes was associated with increased mortality across all cancer types, with greater risk of death for some cancers, including breast cancer.[4]
However, few studies have examined the influence of diabetes on cancer survival in First Nations or any Indigenous population,[5][6] and to our knowledge, this is the first study in Ontario or elsewhere in Canada to do so. The study findings in the published paper, Influence of pre-existing diabetes on survival after a breast cancer diagnosis in First Nations women in Ontario, Canada, indicate that it is important for cancer care teams treating First Nations women with breast cancer to be aware of this survival discrepancy, particularly because incidence rates of breast cancer and type 2 diabetes are increasing in Canada’s First Nations populations.[7][8][9][10]