Impact of Immigration Status on Survival Among Stage 1 and 2 HER2‐Positive and Triple‐Negative Breast Cancer in Ontario, Canada

Background This study examined death from breast cancer and death from other causes among women with Stage 1 and 2 Her2‐positive and triple‐negative breast cancer (BC) by immigration status. Methods We identified women aged 18–75 diagnosed with BC in Ontario from January 1, 2012, to December 31, 2019, followed them to December 31, 2023, and identified legal immigrants from the Immigration, Refugee, and Citizenship Canada Permanent Resident (CIC) database. We linked administrative data sources for the date of diagnosis, molecular subtype, death due to breast cancer, and death due to all other causes. Using adjusted competing risks regression (Fine and Gray method), we analyzed the influence of immigration on breast cancer survival and calculated the sub‐distribution hazard ratios (sHR). Results There was no increased risk of death among legal immigrants on univariate or multivariable analysis. They had a sHR of 0.95 (0.77–1.19) on univariate analysis and 1.06 (95% CI: 0.83–1.36) on multivariable analysis for breast cancer deaths, and for other causes of death, 0.63 (0.47–0.83) on univariate analysis, and 0.85 (95% CI: 0.62–1.15) on multivariable analysis compared to long‐term residents. Patients with HER2‐positive status had a lower risk of death from breast cancer and other causes compared to those with triple‐negative breast cancer (TNBC). Patients with Stage 2 cancer had a significantly higher hazard of death from breast cancer compared to Stage 1 (HR = 3.72, 95% CI: 2.96–4.66, p < 0.0001). Conclusions In Ontario, legal immigrants do not have an increased risk of death from breast cancer or other causes compared to long‐term residents.