21 Jan 2010, 1043 hrs IST

Besides causing lung cancer, repeated exposure to tobacco smoke can promote the growth of pre-existing cancer tumours, say researchers.

Scientists at the University of California, San Diego School of Medicine have found that mice with early lung cancer lesions that were repeatedly exposed to tobacco smoke developed larger tumors - and developed tumors more quickly - than unexposed animals. The key contributing factor was lung tissue inflammation.

The study has been published January 19 in the journal Cancer Cell.

Michael Karin, PhD, Distinguished Professor of Pharmacology and Pathology at the UC San Diego School of Medicine, who led the work, said: "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."

Karin, director of the Laboratory of Gene Regulation and Signal Transduction and a member of the Moores UCSD Cancer Center, added: "Other particulate materials, such as fine silicon dust, asbestos and coal dust, may promote lung cancer development through similar mechanisms. Such substances were never found to induce mutations, which are the essence of tumor formation. More research is needed to explore the role and biochemical mechanisms of exposure to pro-inflammatory substances in the environment in early stages of cancer development."

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