Assignment to either aromatase inhibitors or tamoxifen (defined as first dispensation) was assumed to be random within levels of the baseline covariates: age, year of baseline, time from diagnosis, stage, T classification, N classification, grade, HER2 status, side, chemotherapy, radiotherapy, antibody treatment, cerebrovascular disease, diabetes, COPD, diabetic drugs, anticoagulants, antidepressants, NSAIDs, opioids, hormone replacement therapy, marital status, education status, and employment status (see Table S1 for full definition of all covariates). Here, ERBB2 is linked to diabetes mellitus.