A large new observational study finds more evidence of an association between daily aspirin use and modestly lower cancer mortality, but suggests any reduction may be smaller than that observed in a recent analysis. The study authors say important questions remain about the degree of aspirin's potential benefits.
A recent analysis pooling results from existing randomized trials of daily aspirin for prevention of vascular events found an estimated 37% reduction in cancer mortality among those using aspirin for five years or more. But uncertainty remains about how much daily aspirin use may lower cancer mortality, as the size of this pooled analysis was limited and two very large randomized trials of aspirin taken every other day found no effect on overall cancer mortality.
For the current study, researchers analyzed information from 100,139 predominantly elderly participants in the Cancer Prevention Study II Nutrition Cohort who reported aspirin use, did not have cancer at the study's start, and were followed for up to 11 years. They found daily aspirin use was associated with an estimated 16% lower overall risk of cancer mortality. The lower overall mortality was driven by about 40% lower mortality from cancers of the gastrointestinal tract and about 12% lower mortality from cancers outside the gastrointestinal tract.
The reduction in cancer mortality observed in the current study is considerably smaller than the 37% reduction reported in the recent pooled analysis. The authors note that their study was observational, not randomized, and therefore could have underestimated or overestimated potential effects on cancer mortality if participants who took aspirin daily had different underlying risk factors for cancer than those who did not.