Low-dose aspirin use and survival in breast cancer patients: A nationwide cohort study

•Preclinical evidence suggests low-dose aspirin can delay breast cancer progression.•Some epidemiological studies have been limited by size and time-related biases.•We conducted a nation-wide study of low-dose aspirin and breast cancer mortality.•We did not observe an association between its use and breast cancer mortality.•These findings will help inform decisions to conduct RCTs in breast cancer patients.

BackgroundPreclinical evidence from breast cancer cell lines and animal models suggest that aspirin could have anti-cancer properties. In a large breast cancer patient cohort, we investigated whether post-diagnostic low-dose aspirin use was associated with a reduction in the risk of breast cancer-specific mortality.MethodsWe identified 15,140 newly diagnosed breast cancer patients within the Scottish Cancer Registry. Linkages to the Scottish Prescribing Information System provided data on dispensed medications and breast cancer-specific deaths were identified from National Records of Scotland Death Records. Time-dependent Cox regression models were used to calculate hazard ratios (HR) and 95% CIs for breast cancer-specific and all-cause mortality by post-diagnostic low-dose aspirin use. HRs were adjusted for a range of potential confounders including age at diagnosis, year of diagnosis, cancer stage, grade, cancer treatments received, comorbidities, socioeconomic status and use of statins. Secondary analysis investigated the association between pre-diagnostic low-dose aspirin use and breast cancer-specific and all-cause mortality.ResultsPost-diagnostic users of low-dose aspirin appeared to have increased breast cancer-specific mortality compared with non-users (HR 1.44, 95% CI 1.26, 1.65) but this association was entirely attenuated after adjustment for potential confounders (adjusted HR 0.92, 95% CI 0.75, 1.14). Findings were similar in analysis by increasing duration of use and in analysis of pre-diagnostic low-dose aspirin use.ConclusionIn this large nationwide study of breast cancer patients, we found little evidence of an association between post-diagnostic low-dose aspirin use and cancer-specific mortality.