No survival gain with aspirin in colon cancer

24/11/2013

Colon cancer patients who used low-dose aspirin after their diagnosis didn't see an increase in survival time, researchers found.

In a case-control cohort, there were no significant associations between low-dose aspirin use and colorectal cancer-specific mortality (adjusted odds ratio 1.06, 95% CI 0.92-1.24) or all-cause mortality (aOR 1.06, 95% CI 0.94-1.19) post-diagnosis, according to Chris Cardwell, PhD, of Royal Victoria Hospital in Belfast, Northern Ireland, and colleagues.

Additionally, there was no dose-response association for low-dose aspirin use with colorectal cancer-specific mortality after 1 year (aOR 0.98, 95% CI 0.82-1.19), they wrote online in the journal Gastroenterology.

Numerous previous studies have evaluated aspirin in colorectal cancer patients and found that the anti-inflammatory drug has been associated with improved survival in some colon cancers, possibly due to its antiplatelet activity. Taking aspirin after a colorectal cancer diagnosis has also been shown to reduce risk of recurrence and death in other research, but these effects were not seen in patients who received it prior to the diagnosis.

The authors studied the associations of survival with low-dose aspirin receipt in a nested case-control analysis of 4,794 colorectal cancer patients from the U.K. Clinical Practice Research Datalink after the patients had received a cancer diagnosis.

They compared cases of patients dying of colorectal cancer with age-, sex-, year of diagnosis-, and cancer site-matched controls who lived at least as long after their diagnosis.

Aspirin doses of 75 mg or less were considered low-dose. Duration of therapy was recorded, and tablet consumption was calculated by dividing the number of tablets prescribed over the duration of the exposure period.

Data were adjusted for cancer stage, histological grade and surgery, chemotherapy and radiotherapy, smoking, alcohol consumption, body mass index, statin and metformin use, and comorbidities. Comorbidities included myocardial infarction, cerebrovascular disease, congestive heart disease, chronic pulmonary disease, peripheral vascular disease, peptic ulcer disease, renal disease, rheumatologic disease, and diabetes.

They also conducted a second analysis that restricted data to those from patients with stage and grade of cancer available and with adjustments for stage, grade, and smoking status.

The sample included 1,559 colorectal cancer-specific deaths from the main sample versus 1,453 colorectal cancer-specific deaths in 7,530 matched risk-set controls, 25% of whom used low-dose aspirin.

Mean follow-up was 7.2 years and mean time to death was 3 years.

Patients who died from colorectal cancer in the study had an overall higher disease stage and grade, were more likely to have chemotherapy and radiotherapy, and were less likely to have surgery versus controls. They also had higher rates of smoking, congestive heart failure, and peripheral vascular disease.

There was no link between aspirin use with colon cancer-specific mortality (aOR 1.02, 95% CI 0.83-1.25) or rectal cancer-specific mortality (aOR 1.10, 95% CI 0.88-1.38), the group found.

There also was no difference by cancer site among low-dose aspirin users in lack of association.

The authors noted that their findings were different from outcomes from a Scottish study that reported "marked reductions" in cancer-specific mortality with low-dose aspirin usage after diagnosis (aOR=0.58, 95%CI 0.45-0.75).

They explained that the differences were most likely because of statistical analyses.

"[The Scottish] study used an analysis method (a Cox model with aspirin use as an unlagged start/stop time varying covariate) which would have allocated the cancer-specific deaths to the aspirin user or non-user group on the basis of whether they had an aspirin prescription which covered the date of death," they explained. "Using this analysis technique we get a similar result (adjusted hazard ratio=0.46, 95% CI 0.39-0.55). However, unlagged time varying covariate analyses can bias results due to reverse causality.""

The authors also cautioned that their study was observational and limited by lack of unrecorded variables, as well as incomplete reporting of other variables.

Two trials, ASCOLT and Add Aspirin, will provide further evidence on the effectiveness of aspirin as an adjunct treatment. Results are expected in 2020.

 

Source: MedPage Today: http://www.medpagetoday.com/Gastroenterology/ColonCancer/43092

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