We conducted a prospective cohort study of Nonsteroidal anti-inflammatory d
rugs (NSAIDs) and breast cancer among 32,505 women in central Ohio, USA. Af
ter 5 years of follow-up, a total of 393 cases have been detected. The annu
al incidence of breast cancer per 100,00 women varied inversely with increa
sing intake of NSAIDs, declining from 323 among non-users to 183 among heav
y users (p<0.01). Breast cancer rates decreased by about 50% with regular i
buprofen intake (p<0.01), and by about 40% with regular aspirin intake (p<0
.05). The results suggest that specific NSAIDs may be effective chemopreven
tive agents against breast cancer.