Researchers working with mice say that tobacco smoke, besides causing lung cancer, can promote the growth of pre-existing cancer tumours.

Scientists at the University of California, San Diego School of Medicine found that the inflammation of lung tissue caused by tobacco smoke caused tumours to grow and to develop more quickly.

In their experiment, the researchers caused lung cancer in lab mice by either exposing them to a chemical carcinogen or introducing a mutated gene into their genetic code.

Some of the mice were then intermittently exposed to tobacco smoke.

The researchers found that mice with early cancer lesions that were exposed to the smoke developed large tumours that grew more quickly than in those mice that were not exposed to the smoke.

"We've shown for the first time that tobacco smoke is a tumor promoter — not only a tumor initiator — and that it works through inflammation," said Michael Karin of UC San Diego in a statement.

To determine that it was the inflammation that was leading to the increased cancer growth, the scientists deactivated a chemical signal in the mice, called nuclear factor kappa B, that's known to be a common link between inflammation and cancer.

In mice where the chemical signal was deactivated, the tobacco smoke didn't cause lung inflammation and didn't promote the growth of cancer tumours.

The researchers said that if studies in humans reveal that tobacco smoke triggers the same chemical signals that they do in mice, there could be a case for using anti-inflammatory drugs in patients with early stage lung cancer.

Lung cancer remains the leading cause of cancer death for both men and women in Canada.

Every year, 20,000 Canadians develop lung cancer, but by the time symptoms emerge it's usually too late to treat, which is why 95 per cent of patients don't survive. Worldwide, lung cancer kills around one million people each year.

The research was published Tuesday in the journal Cancer Cell.