Researchers have identified two single nucleotide polymorphisms (SNPs) that can provide differential benefit for aspirin use in relation to colorectal cancer risk.

It is well known that aspirin or nonsteroidal anti-inflammatory drug (NSAID) can reduce the risk of colorectal cancer. But doctors were reluctant to use NSAIDs for cancer prevention without a better understanding of why the drugs seem to work.

The reason was that for some people the same pills make colorectal cancer more likely. The research was done to know how to separate people who will be benefitted from asprin and those who won't be. The researchers looked at three specific spots in the vast human genome to find this out.

A research team lead by Hongmei Nan, M.D., Ph.D., from Indiana University in Indianapolis conducted a case-control study using data from studies that involve 8,634 colorectal cancer cases and 8,553 matched controls.

The researchers tested gene × environment interactions between regular use of aspirin or nonsteroidal anti-inflammatory drug (NSAID) in relation to colorectal cancer risk.

The analysis of the overall data revealed that regular use of aspirin reduces the risk of colorectal cancer with nonregular use.

The researchers identified three intriguing SNPs after crunching a ton of data. When people had the common versions of these SNPs, the use of asprin was associated with reduced risk of colorectal cancer.

But when people had uncommon versions of these SNPs, taking the drugs increased the risk of colorectal cancer.

The first of these SNPs is known as rs2965667 and the second SNP is known as rs10505806. Both are located on chromosome 12. The third relevant SNP was rs16973225, on chromosome 15.

The locations of these SNPs gave researchers some clues about how the painkillers might be fighting colorectal cancer. Among individuals with two less common genotypes of rs16973225 (AC or CC, 9% of participants), no association was found between regular use and risk of colorectal cancer.