Long-term Aspirin Use Reduces Risk For Colorectal Cancer

"Severalearlier studies have found that, among patients with a history of colonpolyps or cancer, regular aspirin treatment prevents the recurrence ofprecancerous polyps. However, the ability of aspirin to reduce thelong-term incidence of invasive cancer has not been well-demonstrated,"says Andrew Chan, MD, MPH, of the MGH Gastrointestinal Unit, thepaper's lead author. "Our study did find a protective effect oflong-term aspirin use on risk of invasive colorectal cancer, but onlyat dosage levels considerably higher than those used to preventcardiovascular disease."

The Nurses' Health Study (NHS) hasfollowed more than 120,000 female registered nurses since themid-1970s, asking them to complete a questionnaire on risk factors forand incidence of cancer and cardiovascular disease every two years. In1980, assessments of diet and the use of aspirin and NSAIDS were added.The current report analyzes information from almost 83,000 NHSparticipants, among which 962 cases of colorectal cancer were diagnosedduring the 20-year study period.

While the incidence ofcolorectal cancer was lower in the women who took aspirin regularly,the risk reduction was significant only for those taking aspirin 10years or longer. The benefit increased as dosage levels rose, with thegreatest risk reduction seen in those taking more than 14 standardtablets per week. A similar risk reduction was seen with the intake ofNSAIDS, with greater benefit also associated with higher dosage; but ananalysis of acetaminophen, which is believed to act through differentmechanisms, found no association of that medication with colorectalcancer. It is believed that the ability of aspirin and NSAIDS to reducecancer risk may, at least in part, relate to their shared ability toinactivate the COX-2 enzyme, which could stimulate tumor development.

Therisk of serious gastrointestinal bleeding, a known side effect of bothaspirin and NSAIDS, also rose as dosage levels increased, with bleedingoccurring nearly twice as often in those taking the highest doses. Theresearchers estimate that a high-dose aspirin regimen that preventedone or two cases of colorectal cancer in a population might alsocontribute to eight additional cases of serious gastrointestinalbleeding.

"Before we can make any recommendations about whetherpatients should take these medications to reduce their cancer risk,we're going to need additional studies that clarify the risks andbenefits of such an approach, particularly compared to other preventionstrategies. For now, individuals need to discuss the options with theirphysicians" says Chan, who is an instructor in Medicine at HarvardMedical School. Chan and his colleagues have already initiated studiesaimed to further clarify the impact of long-term use of aspirin andNSAID drugs, particularly in those at high risk for cancer and otherchronic diseases.

Additional authors of the study are CharlesFuchs, MD, MPH, senior author, of Dana-Farber Cancer Institute andBrigham and Women's Hospital (BWH); Edward Giovannucci, MD, ScD, EvaSchernhammer, MD, DrPH, and Gary Curhan MD, ScD, all of BWH and theChanning Laboratory at Harvard Medical School; and Jeffrey Meyerhardt,MD, MPH, of Dana-Farber. The study was supported by grants from theNational Cancer Institute, the National Institutes of Health, theAmerican Gastroenterological Association and the Foundation forDigestive Health.

The Nurses' Health Study (NHS) was initiated in1976 at BWH. The NHS is the longest-running, major women's health studyever undertaken and has resulted in hundreds of journal articles, manycontaining groundbreaking findings on how to prevent some of the majorcauses of disease and death in women.

Massachusetts GeneralHospital, established in 1811, is the original and largest teachinghospital of Harvard Medical School. The MGH conducts the largesthospital-based research program in the United States, with an annualresearch budget of more than $450 million and major research centers inAIDS, cardiovascular research, cancer, cutaneous biology, medicalimaging, neurodegenerative disorders, transplantation biology andphotomedicine. In 1994, MGH and Brigham and Women's Hospital joined toform Partners HealthCare System, an integrated health care deliverysystem comprising the two academic medical centers, specialty andcommunity hospitals, a network of physician groups, and nonacute andhome health services.