Patterns of comorbidities in women with breast cancer: a Canadian population-based study.

PURPOSE: Improving the understanding of co-existing chronic diseases prior to and after the diagnosis of cancer may help to facilitate therapeutic decision making in clinical practice. This study aims to examine patterns of comorbidities in Canadian women with breast cancer. METHODS: We conducted a retrospective cohort study using provincial linked administrative health datasets from British Columbia, Canada, between 2000 and 2013. Women diagnosed with breast cancer between 2005 and 2009 were identified. The index date was defined as the date of diagnosis of breast cancer. Subsets of the breast cancer cohort were identified based on the absence of individual type of comorbidity of interest within 5 years prior to breast cancer diagnosis. For each subset, cases were then individually matched by year of birth at 1:2 ratios with controls without a history of cancer and the individual type of comorbidity of interest within 5 years prior to the assigned index year, matching with the year of breast cancer diagnosis of the corresponding case. Baseline comorbidities were measured over a 1-year period prior to the index date using two comorbidity indices, Rx-Risk-V and Aggregated Diagnosis Groups (ADG). Cox regression model was used to assess the development of seven specific comorbidities after the index date between women with breast cancer and non-cancer women. 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/pain-inflammation (34.8%). The most prevalent category measured using the ADG model was major signs or symptoms (71.8%), followed by stable chronic medical conditions (52.2%). The risks of developing ischemic heart disease, heart failure, depression, diabetes, osteoporosis, and hypothyroidism were higher in women with breast cancer compared to women without cancer, with the hazard ratios ranging from 1.09 (95 CI% 1.03-1.16) for ischemic heart disease to 2.10 (95% CI 1.99-2.21) for osteoporosis in the model adjusted for baseline comorbidity measured using Rx-Risk-V score. CONCLUSION: Women with breast cancer had a higher risk of developing new comorbidities than women without cancer. Development of coordinated care models to manage multiple chronic diseases among breast cancer patients is warranted.