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Low-dose aspirin and incidence of colorectal tumors in a randomized trial . BACKGROUND Laboratory , clinical , and epidemiologic studies have recently suggested that regular use of aspirin can reduce colorectal cancer incidence or mortality . However , observational epidemiologic analyses have had limited opportunity to control for confounding bias or to specify aspirin doses used . PURPOSE Our purpose was to examine the relationship between regular use of low-dose aspirin and incidence of invasive and noninvasive colorectal tumors by utilizing data from the Physicians ' Health Study , a randomized , double-blinded , placebo-controlled trial of aspirin and beta carotene . We also attempted to determine whether invasive cancers among aspirin users were associated with rectal bleeding and early stage at diagnosis . METHODS The Physicians ' Health Study includes 22071 U.S. male physicians . The aspirin arm was terminated in 1988 after a mean follow-up of 5 years . Stage at diagnosis and signs and/or symptoms during presentation were abstracted from medical records . Cox proportional hazards models were used to estimate relative risk ( RR ) , 95 % confidence intervals ( CIs ) , and the association between aspirin and bleeding . Differences between aspirin and placebo groups in tumor risk over time were visualized with Kaplan-Meier curves . We assessed the association between aspirin and stage at diagnosis with a Mann-Whitney rank sum statistic for non-parametric comparison of two ordinal distributions . RESULTS The RR of developing colorectal cancer for aspirin compared with placebo was 1.15 ( 95 % CI = 0.80-1.65 ) . For in situ cancers and polyps , the RR was 0.86 ( 95 % CI = 0.68-1.10 ) . There was no significant trend for decreasing RR by year of follow-up for invasive cancers ( P = .09 ) or noninvasive tumors ( P = .96 ) . Aspirin and placebo groups did not differ in stage or prevalence of rectal bleeding at diagnosis . CONCLUSIONS Regular aspirin use , at a dose adequate for preventing myocardial infarction , was not associated with a substantial reduction in the incidence of colorectal cancer during 5 years of randomized treatment and follow-up . A small decrease in polyps in the aspirin group could not be reliably distinguished from a chance association . Our results suggest that among low-dose aspirin users , ( a ) colorectal cancer mortality is not likely to be reduced by earlier detection and ( b ) incidence is not likely to be increased due to aspirin-induced gastrointestinal bleeding . IMPLICATIONS The potential for a benefit from higher doses of aspirin or longer duration of use should be addressed by more detailed observational epidemiologic studies and prevention trials with longer follow-up of randomized participants .
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Intervention_Pharmacological
Low-dose aspirin
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Intervention_Pharmacological
aspirin
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Intervention_Pharmacological
aspirin
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Intervention_Pharmacological
low-dose aspirin
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Intervention_Control
placebo-controlled
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Intervention_Pharmacological
aspirin
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Intervention_Pharmacological
beta carotene
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Intervention_Pharmacological
aspirin
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Intervention_Pharmacological
aspirin
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Intervention_Control
placebo
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Intervention_Pharmacological
aspirin
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Intervention_Pharmacological
aspirin
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Outcome_Physical
relative risk
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Outcome_Other
confidence intervals
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Outcome_Physical
RR
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Outcome_Adverse-effects
rectal bleeding
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Outcome_Physical
colorectal cancer
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Participant_Sample-size
22071
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Participant_Sex
male