This was a prospective observational study based on responses from 4,164 female registered
nurses in the Nurses’ Health Study who were diagnosed with stages I, II, or III breast cancer
between 1976 and 2002 and were observed until death or June 2006, whichever came first. The
main outcome was breast cancer mortality risk according to number of days per week of aspirin
use (0, 1, 2 to 5, or 6 to 7 days) first assessed at least 12 months after diagnosis and updated.