Aspirin can help extend lives of people who have colorectal cancer, but only of those who have a certain genetic mutation in their tumor, reports the Harvard Gazette.

Physicians have prescribed aspirin to people who have colorectal cancers for long, but not all patients got the same benefits of using the drug. The current research explains that the increased efficacy of the drug seen in some cancer survivors is due to a single genetic mutation in the tumor. Researchers say that people without the genetic mutation can be given aspirin, but the drug won't be as effective.

The study was conducted on 900 patients who were diagnosed with colorectal cancer. Use of aspirin was associated with longer survival period in people who had tumors with specific mutation in the gene PIK3CA. About 97 percent of these people lived five years or longer after using aspirin compared to some 74 percent of people who weren't using aspirin.

"Our results suggest that aspirin can be particularly effective in prolonging survival among patients whose colorectal cancer tests positive for a mutation in PIK3CA. For the first time, we have a genetic marker that can help doctors determine which colorectal cancers are likely to respond to a particular therapy," said the study's senior author, Shuji Ogino of Dana-Farber, Brigham and Women's Hospital, and the Harvard School of Public Health.

Ogino added that further research is needed to verify the study results.

Colorectal cancers - cancers that affect colon and rectum - are the fourth most common cancer in both men and women in the U.S. According to estimates by the National Cancer Institute, 103,170 new cancers of colon and 40,290 of rectum will be diagnosed in the year 2012.

A study published in the Lancet last year had said that people who have genetically susceptible to the cancer (where the cancer runs in the family) can reduce their risk of the cancer by using 600 mg of aspirin per day for 25 months. Another study published in Gastroenterology in 2008 said that men can lower the risk of colorectal cancer by using aspirin continuously for 6 years with about 14 tablets per week, a really high dose that may lead to other health problems.