To date, no prospective studies have explored the relationship between the use of
aspirin, other nonsteroidal anti-inflammatory medications (
NSAID), and
acetaminophen and endometrial
adenocarcinoma. Of the 82,971 women enrolled in a prospective cohort study, 747 developed medical record-confirmed invasive
endometrial cancer over a 24-year period. Use of
aspirin was ascertained from 1980 to 2004, and for other
NSAIDs and
acetaminophen, from 1990 to 2004. Cox regression models calculated multivariate relative risks (MV RR), controlling for body mass index (BMI), postmenopausal
hormone (PMH) use, and other
endometrial cancer risk factors. Currency, duration, and quantity of
aspirin were not associated with
endometrial cancer risk overall [current use: MV RR, 1.03; 95% confidence interval (CI) 0.83-1.27; >10 years of use: MV RR, 1.01; 95% CI, 0.78-1.30; and cumulative average >7
tablets per week: (MV RR, 1.10; 95% CI, 0.84-1.44)]. However, stratified analyses showed that a lower risk of
endometrial cancer among obese (BMI, >or=30 kg/m(2)) women was seen with current
aspirin use (MV RR, 0.66; 95% CI, 0.46-0.95). The greatest risk reduction for current
aspirin users was seen in postmenopausal obese women who had never used PMH (MV RR, 0.43; 95% CI, 0.26-0.73). The use of other
NSAIDs or
acetaminophen was not associated with
endometrial cancer. Our data suggest that use of
aspirin or other
NSAIDs does not play an important role in
endometrial cancer risk overall. However, risk was significantly lower for current
aspirin users who were obese or who were postmenopausal and had never used PMHs; these subgroup findings require further confirmation.