Regular aspirin use and breast cancer risk in US Black women

Epidemiologic studies have yet to provide consistent evidence to support a protective effect of aspirin and other non-steroidal anti-inflammatory drugs (NSAID) on the incidence of breast cancer.

We evaluated the relations of current use of aspirin, non-aspirin NSAIDs, and acetaminophen with breast cancer incidence in the Black Women's Health Study.

Biennial follow-up of 59,000 study participants began in 1995. During 558,600 person-years of follow-up through 2007, 1,275 breast cancer cases were identified. Using Cox proportional hazards regression, we estimated incidence rate ratios (IRR) and 95% confidence intervals (CI) for associations of current and former use of aspirin, other NSAIDs, and acetaminophen with incident breast cancer.

After adjustment for age, education, body mass index at age 18, physical activity, female hormone use, current smoking, and other NSAID use, the IRRs were 0.79 (95% CI = 0.66, 0.95) for current aspirin use and 0.68 (95% CI = 0.50, 0.92) for ≥5 years of aspirin use. Similar associations were observed for acetaminophen use.

Both aspirin and acetaminophen use were inversely associated with breast cancer incidence in the present study. Reasons for the association with acetaminophen use are unclear, given that acetaminophen has very weak anti-inflammatory effects.