New data on aspirin and colorectal cancer brings calls for new guidelines, more research.

T hree large studies in the past 14 months have reopened a longstanding issue in colorectal cancer: Can aspirin prevent it? Or more precisely, is the evidence for preventive benefit in people at average risk strong enough to outweigh the known risks of regular aspirin use? Up to now, the committees that draw up cancer prevention guidelines have concluded that the evidence for aspirin ’ s benefi ts was insuffi cient when weighed against the risk of gastrointestinal bleeding, a common side effect that can be severe; aspirin can also cause hemorrhagic stroke. But the new studies, though not perfect, could tip the scales in favor of aspirin, say some experts. The accumulated data now “arguably support more general recommendations to consider aspirin for prevention of colorectal cancer in the context of individualized risk-benefi t assessments,” wrote Andrew Chan, M.D. Harvard Medical School, Boston, and Scott Lippman, M.D. at the M.D. Anderson Cancer Center in Houston, in their Lancet editorial on December 17 th . “We ’ re in a situation where no single study will settle all the questions for everyone,” Chan said in an interview. “But a lot of evidence is in and we’ve reached a point where there is a suffi cient body of evidence for us to no longer question if aspirin can prevent colorectal cancer, but to decide what kind of risk stratifi cation we need.” Others argue that the evidence is still not strong enough, pointing to weaknesses in the new studies. Nevertheless, it seems certain that guideline committees will revisit the issue in 2012 and that ongoing research on aspirin ’ s risks and benefi ts in cancer prevention has taken on new visibility.