Colon Ca deaths cut by postdiagnosis aspirin.(NEWS)(cancer)(Clinical report)

CHICAGO -- The regular use of aspirin after a diagnosis of colorectal cancer significantly decreases the risk of colon cancer--specific death, especially in patients with cyclo-oxygenase-2--positive tumors.

Patients with COX-2--positive tumors who began taking aspirin after their diagnosis were three times less likely to die from their cancer than were patients with COX-2--negative tumors, for a relative risk reduction of 61%, Dr. Andrew T. Chan reported at the annual Digestive Disease Week.

"We did see a very modest dose-response relationship," Dr. Chan said, although the dose did not significantly affect the risk reduction. The benefit appeared even in those taking very low doses.

It's unclear exactly how aspirin interacts with the tumor to improve survival, said Dr. Chan of Massachusetts General Hospital, Boston. It may alter the biology of COX-2--positive tumors or prevent their recurrence. "The data suggest that there is a potential for using COX-2 markers to tailor our treatment of colorectal cancer," he added.

Dr. Chan and his colleagues previously showed that regular aspirin use decreases the risk of developing colorectal cancers, particularly those that overexpress COX-2 (N. Engl. J. Med. 2007; 356:2131-42).

Drawing on the same two cohorts, the investigators then sought to determine aspirin's effect on survival when initiated after a diagnosis of colorectal cancer. "A key feature of this study was that the patients were enrolled before diagnosis of colorectal cancer, so we were able to assess the intake of aspirin before and after diagnosis," Dr. Chan said.

The two prospective cohort studies comprised almost 174,000 men and women with a mean follow-up time of 12 years. During that period, 1,279 participants developed colorectal cancer. There were 480 deaths, 222 of which were from colorectal cancer. Among those who did not use aspirin (730) there were 141 colorectal cancer deaths. Among aspirin users (549), there were 81 colorectal cancer deaths.

The investigators conducted a multivariate analysis that controlled for age at cancer diagnosis, cancer stage at diagnosis, rate of tumor growth, site of tumor, body mass index, smoking, and physical activity.

Compared with nonusers, those who regularly used aspirin after their cancer diagnosis were 28% less likely to die from their cancers (hazard ratio 0.72). In a subset of 719 patients who did not use aspirin regularly before their diagnosis but who began using it afterward, cancer-specific risk of death was 45% lower than in nonusers.

COX-2 immunohistochemistry was available for 459 tumors; 314 were positive and 145 were negative.

Among the COX-2--positive tumors, regular aspirin use after diagnosis was associated with a statistically significant 61% decrease in the risk of cancer-specific death (HR 0.39). Aspirin use had little effect on COX-2--negative tumors (HR 1.25).

Dr. Chan said he had no conflicts of interest with regard to the study.

VERBATIM

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