Blood pressure and risk of breast cancer, overall and by subtypes: a prospective cohort study.

OBJECTIVE: Blood pressure (BP) and breast cancer may share a common pathophysiologic pathway involving chronic inflammation, hormone synthesis and metabolism. Previous studies investigating the association between BP and breast cancer measured BP at a single time point and did not examine associations by breast cancer molecular subtypes.

METHODS: We used data from 22 833 female participants in the Melbourne Collaborative Cohort Study. BP was objectively measured at baseline (1990-1994) and a follow-up visit (2003-2007). Cox regression was used to estimate hazard ratios for baseline BP and temporal changes in BP in relation to risk of breast cancer, overall and by molecular subtypes.

RESULTS: We did not observe any associations between BP measured at baseline and breast cancer risk overall (per 5 mmHg SBP, hazard ratio = 1.00, 95% confidence interval: 0.99-1.02), nor by subtype (per 5 mmHg SBP: estrogen-receptor-negative: hazard ratio = 0.99, 0.96-1.03, progesterone-receptor-negative: hazard ratio = 1.01, 0.99-1.04, human epidermal growth factor receptor 2 negative: hazard ratio = 1.00, 0.98-1.01). Temporal changes in BP were not associated with risk of breast cancer (per 5 mmHg change in SBP, hazard ratio = 1.00, 0.97-1.03). Increased DBP over time was associated with higher risk of triple-negative breast cancer (P = 0.04), based on a small number of cases (N = 41).

CONCLUSION: Our study supports previous findings of no association between BP and breast cancer. Similar conclusions were reached when assessing BP over time and when examining specific tumor subtypes.