Factors associated with early death from de novo metastatic breast cancer in Ontario, Canada

Background — Early death from female breast cancer is influenced by disease biology and factors such as age, marginalization, socioeconomic status, rurality, and access to primary care. Our objective was to investigate factors associated with early death in the subgroup of patients diagnosed with advanced de novo metastatic breast cancer, defined by the presence of distant metastatic disease at initial presentation.

Methods — We used linked health care administrative data from Ontario, Canada, from 2010 to 2019 to conduct a population-based retrospective cohort study. We identified adults diagnosed with de novo metastatic breast cancer through the Ontario Cancer Registry. The primary outcome was the frequency of early death, defined as death within 6 months of cancer diagnosis. We used a multivariable logistic regression model to determine the patient, cancer, and provider characteristics associated with early death.

Results — Among 4004 patients diagnosed with de novo metastatic breast cancer, 22.9% (n = 918) experienced early death. A higher Ontario Marginalization Index score for the domains of households and dwellings, and material resources was significantly associated with early death (odds ratio [OR] 1.27, 95% confidence interval [CI] 1.04 to 1.55, and OR 1.21, 95% CI 1.00 to 1.46, respectively). Registration with a primary care physician was associated with significantly decreased odds of early death (OR 0.74, 95% CI 0.62 to 0.88). We observed variability in early death across geographic regions and an increase in early death among patients living in rural areas after the start of systemic therapy.

Interpretation — Marginalization, access to a primary care physician, and geography play a role in early death in patients diagnosed with de novo metastatic breast cancer in Ontario. Improving access to primary care providers may help reduce early death in these patients.