Smokers at increased risk for colon cancer

SAN DIEGO, April 14 (UPI) -- Smoking puts older women at risk for loss of DNA repair proteins that are critical for defending against some colorectal cancers, a U.S. study found.

A research team led by Mayo Clinic scientists found that women who smoked were at increased risk for developing colorectal tumors that lacked some or all of four proteins, known as DNA mismatch repair, or MMR, proteins. These proteins keep cells lining the colon and rectum healthy because they recognize and repair genetic damage, as well as mistakes that occur during cell division.

Lead author gastroenterologist Dr. Paul Limburg said researchers believe that, in this study population, few if any of the four proteins were absent because of an inherited genetic alteration.

"We think that smoking induces a condition within intestinal cells that does not allow MMR genes to express their associated proteins, and this loss leads to formation of tumors in some women," Limburg said.

"Our findings suggest that tumors may form because cells can't repair themselves from damage induced by smoking. Tobacco toxins appear to block the DNA repair genes from producing their beneficial proteins."

The study is being presented at the annual meeting of the American Association for Cancer Research in San Diego.