Individual-level health inequalities in breast cancer stage and survival in Northern Ireland: a population-based cohort study

Abstract Background Understanding the impact of health inequalities on breast cancer presentation, treatment and survival is important. This study investigated individual-level health inequalities on stage at diagnosis and mortality. Methods Women newly diagnosed with breast cancer in Northern Ireland from 2011 to 2021 were identified from cancer registry records. A representative sample were linked to records of potential health inequalities from the 2011 Northern Ireland census. Breast cancer-specific death up to March 2023 was the primary outcome. Adjusted hazard ratios (HRs) and 95% confidence intervals (95% CIs) for cancer-specific death by categories of health inequality were calculated using Cox regression after adjusting for confounders. Similarly, the proportion with stage 4 disease was investigated using logistic regression. Results The cohort included 3,892 women with breast cancer. Women with one or more disability, compared with none, had lower odds of stage 4 disease (adjusted odds ratio = 0.64 95% CI 0.46, 0.91; P = 0.012). The odds of stage 4 disease across socio-economic classification categories were similar. Women with one or more disability, compared with none, had a similar rate of breast cancer-specific death (adjusted HR = 1.08 95% CI 0.89, 1.32), but women with hearing disabilities had an increased rate (adjusted HR = 1.36 95% CI 1.04, 1.78). Women from lower socio-economic classification categories had higher rates of breast cancer-specific death (e.g. the adjusted HR for routine or semi-routine versus managerial occupations was 1.34 95% CI 1.05, 1.72). Conclusions In this cohort several health inequalities, including lower socio-economic classification and hearing disabilities, were associated with worse breast cancer outcomes.