Lung-cancer patients who use nicotine supplements such as 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 laboratory 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, XIAP and survivin, 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.

The findings also were being presented at the annual meeting of the American Association for Cancer Research in Washington.

For smokers with lung cancer, "the best thing is to stop as soon as they can," Chellappan said in a telephone interview. 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."

Dr. John Stevens, a vice president of the American Cancer Society, said if there were anyway that someone "could be induced to quit without using nicotine substitutes, then that would be my suggestion.

"However, if there is no other way, I would opt for the lesser of two evils, and the lesser is to quit smoking by whatever means," Stevens, who was not part of the research team, said in a telephone interview.

Dr. Nithya Ramnath, a lung-cancer specialist at the Roswell Park Cancer Institute in Buffalo, N.Y., agreed on the need for lung-cancer patients to stop smoking. But Ramnath stopped short of saying they should avoid using things such as a nicotine patch to help them do so.

The research was done in a laboratory and it can be a leap of faith to assume that it would work the same in humans, said Ramnath, who was not part of Chellappan's team.

"At this point we tell patients we do know that treatment effects are going to be worse if they continue to smoke," she said in a telephone interview. "We tell them absolutely to stop smoking."

Chellappan's research adds detail to earlier findings by Dr. Phillip A. Dennis of the National Cancer Institute.