Washington ? Lung-cancer patients who use nicotine supplements such a patch or gum to help them quit smoking may undermine their chemotherapy.

Nicotine is not known to cause cancer, but it can protect cancer cells from some of the most widely used chemotherapy drugs, researchers reported Sunday at a cancer meeting.

Srikumar Chellappan of the University of South Florida and colleagues studied the effects of nicotine on lung cancer cells that were treated with three commonly used drugs in cancer therapy – gemcitabine, cisplatin and taxol.

The lab research focused on human nonsmall cell lung cancer, which accounts for 80 percent of all lung cancers. In chemotherapy, exposure to the chemicals causes cancer cells to self-destruct in a process called apoptosis.

When nicotine was present, the cells increased production of a pair or proteins that protected the cells from apoptosis.

“Our findings are in agreement with clinical studies showing that patients who continue to smoke have worse survival profiles than those who quit before treatment,” the researchers said.

“They also raise the possibility that nicotine supplementation for smoking cessation might reduce the response to chemotheraputic agents,” they added in a report appearing in next week’s online edition of Proceedings of the National Academy of Sciences.

For smokers with lung cancer, “the best thing is to stop as soon as they can,” Chellappan said. They should avoid nicotine in all forms, not just smoking, he said, adding “that is easier said than done.”

“There are a lot of smoking cessation programs, behavioral rather than chemical based,” he noted. “That would be the best thing to quit smoking.”