Aims: To examine patterns of comorbidity in Canadian women with breast cancer prior to cancer diagnosis; to compare the development of new comorbidities between women with breast cancer and women without history of cancer.
Methods: We conducted a retrospective cohort study using provincial linked administrative health datasets from British Columbia (BC), Canada, for the period between January 2000 and December 2013. Women diagnosed with breast cancer between January 2005 and December 2009 were identified from the BC Cancer Registry. Baseline comorbidities prior to breast cancer diagnosis were evaluated using two comorbidity indices, Rx-Risk-V and Aggregated Diagnosis Groups (ADG). The breast cancer cohort was matched by age and sex at 1:2 ratios with specific control groups without a history of cancer and the individual type of comorbidity of interest evaluated at baseline. Cox regression model was used to assess the development of seven individual comorbidities over time between women with breast cancer and non-cancer women. Death was treated as a competing risk to derive sub-distribution hazard ratios.
Results: The most prevalent baseline comorbidity in the breast cancer cohort measured using the Rx-Risk-V model was cardiovascular conditions (39.0%), followed by pain or pain-inflammation (34.8%). The most prevalent category measured using the ADG model was major sign or symptoms (71.8%), followed by stable chronic medical condition (52.2%). The risks of developing diabetes, depression, osteoporosis, heart failure, ischemic heart disease and thyroid disorder were higher in women with breast cancer compared to women without history of cancer. The risks for depression, heart failure and ischemic heart disease were highest in the first year and declined over time.
Conclusion: Women diagnosed with breast cancer had a higher risk of developing selected new comorbidities than women without history of cancer. Development of coordinated care models to manage multiple chronic diseases among breast cancer survivors is warranted.