Risk of Breast Cancer After Onset of Type 2 Diabetes: Evidence of detection bias in postmenopausal women

OBJECTIVE: To examine the risk of breast cancer in pre- and postmenopausal women with type 2 diabetes (T2D). RESEARCH DESIGN AND METHODS: This was a population-based retrospective cohort study. Cox regression, stratified by pre- (<55 years) and postmenopausal (≥55 years) status, was used to estimate hazard ratios (HRs) for breast cancer, during earlier (0–3 months) and later (3 months to 10 years) time windows after diabetes index date. RESULTS: Compared with women without T2D, HRs for breast cancer were 0.95 (95% CI 0.48–1.86; P = 0.88) and 1.31 (0.92–1.86; P = 0.14) in pre- and postmenopausal women with T2D, respectively, in the early time window, and 0.92 (0.75–1.13; P = 0.45) and 1.00 (0.90–1.11; P = 0.93) in pre- and postmenopausal women with T2D, respectively, in the later time window. CONCLUSIONS: We observed a trend toward an increased risk of breast cancer in postmenopausal women with T2D, but only in the time period immediately after diabetes index date.