Low-dose aspirin in colorectal cancer patients did not increase survival time, a study found.
Researchers in England did a nested case-control analysis of nearly 4,800 patients who had been diagnosed with colorectal cancer from 1998 through 2007. There were nearly 1,600 colorectal cancer-specific deaths, each of which was matched with up to 5 risk-set controls (more than 7,500 total matched risk-set controls).
Results appeared online Nov. 18 in Gastroenterology.
Low-dose aspirin was not associated with colorectal cancer-specific mortality (25.3% versus 26.3%; adjusted odds ratio [OR], 1.06; 95% CI, 0.92 to 1.24) or all-cause mortality (adjusted OR, 1.06; 95% CI, 0.94 to 1.19).
And, there was no dose-response association. Low-dose aspirin use for more than 1 year after diagnosis was not associated with colorectal cancer-specific mortality (adjusted OR, 0.98; 95% CI, 0.82 to 1.19). Also, there was no association between low-dose aspirin and either colon cancer-specific mortality (adjusted OR, 1.02; 95% CI, 0.83 to 1.25) or rectal cancer-specific mortality (adjusted OR, 1.10; 95% CI, 0.88 to 1.38).
Researchers noted the results contrast with 2 previous published results, the Nurses Health and Nurses Health and Health Professionals Follow-up studies, and a Scottish study published in 2013. The likely cause was the statistical analysis used by the previous studies, a Cox model that would have allocated the cancer-specific deaths to the aspirin user or non-user group on the basis of whether the patient had an aspirin prescription that covered the date of death. This study would have had similar results had it used the same method (adjusted hazard ratio, 0.46; 95% CI, 0.39 to 0.55).
They wrote, “The marked drop in aspirin prescriptions prior to death (for instance, 9% of patients are on low-dose aspirin at death compared with 14% 6 months earlier) suggest that dying patients have aspirin prescriptions discontinued (and therefore that an unlagged analysis will artificially create/exaggerate protective effects) or that aspirin exerts a short term protective effect on cancer-specific mortality. Whilst the latter is possible, this seems unlikely as low-dose aspirin is thought to work by preventing metastasis.”