By David Liu PHD

Saturday Aug 25, 2012 (foodconsumer.org) -- Tobacco smoking is known to raise the risk of colorectal cancer.  But a study in the American Journal of Gastroenterology suggests that among women, those who carry certain mutation are not susceptible to this risk induced by tobacco smoke.

The study led by N.J. Samadder of University of Michigan Medical School in Ann Arbor, Michigan and colleagues found many tobacco smoking variables were associated with increased risk of KRAS mutation-negative colorectal cancer, but not the mutation positive tumors.

The study was based on 1,233 patients with colorectal cancer registered in the IOWA Cancer Registry, who were part of a population-based cohort study of cancer incidence among 41,836 randomly selected Iowa women aged 55 to 69 years of age at baseline in 1986.

For the study, participants self-reported their habits of tobacco smoking at baseline, and the researchers had archived tissue specimens from colorectal cancer cases recorded through 2002, analysed for tumor KRAS mutation status.

The researchers found the risk of developing KRAS mutation negative colorectal cancer was associated with age at initiation of tobacco smoking, average number of cigarettes per day, and cumulative pack-years among other things.  But these variables were not correlated with KRAS mutation positive colorectal cancer.

Women who smoked equal to or greater than 40 cigarettes per day on average were 2,38 times as likely as those who never used tobacco to develop the KRSA mutation negative colorectal cancer.

KRAS gene performs an important function in tissue signalling and the mutation of this gene has been associated with a number of cancers.  The significance of this mutation has been recognized in the treatment of colorectal cancer.   According to wikipedia, colorectal cancer with KRAS mutation does not respond well to panitumumab (Vectibix®) and cetuximab (Erbitux®) therapy.

Nothing can be done to change one person's KRAS mutation status. But quitting tobacco use is one thing smokers can do to reduce risk of colorectal cancer.  Another important thing everyone can do to reduce the risk is to follow a healthy diet which is featured with high intake of fiber-rich foods like whole grains and green leafy vegetables and low intake of fat and meat.

Colorectal cancer is expected to be diagnosed in about 150,000 men and women in 2012 in the United States and the disease (colon cancer and rectal cancer combined) will kill 51,690 Americans in 2012, according to the National Cancer Institute.