Mexican researchers say wood smoke may cause lung cancer in nonsmokers.

Javier Delgado, MSc, and colleagues report the finding in Chest. They work at Mexico's Instituto Nacional de Enfermedades Respiratorias.

Most of the nonsmoking lung cancer patients they saw were rural Mexican women living in poverty. They had burned wood for many hours a day for more than a decade.

That's very different from gathering around the hearth occasionally.

"Tobacco smoke is still considered the main cause of lung cancer," write the researchers.

About Lung Cancer

Lung cancer is the No. 1 cause of cancer deaths for men and women alike, according to the American Cancer Society (ACS).

The ACS predicts that there will be more than 172,000 new cases of lung cancer in the U.S. this year.

Smoking is "by far" the leading risk factor for lung cancer, states the web site of the ACS.

Visit WebMD's "Quiz: How Much Do You Know About Lung Cancer?"

Wood Smoke Study

Delgado's team doesn't question the threat posed by tobacco smoke. But other factors could also play a role in lung cancer, they write.

They studied 62 lung cancer patients. Six women and 17 men had smoked tobacco for more than 10 years.

An additional 22 women and two men were nonsmokers who had been exposed to wood smoke for an average of 44 years. They used traditional wood-burning stoves in their kitchens -- with no chimney to let the smoke out of the house.

"We found that 38.7 percent of the lung cancer patients examined were nonsmokers with a history of continuous wood exposure for more than 10 years," write the researchers.

Read WebMD's "Newly Diagnosed with Lung Cancer? Start Here"

Genetic Impact?

The patients' blood samples were checked.

For comparison, blood samples from nine healthy nonsmokers without wood exposure were also screened. So were samples from nine people with chronic obstructive pulmonary disease (COPD).

The nonsmoking, wood-burning lung cancer patients had higher levels in their blood of certain proteins linked to cancer development.

Wood smoke, like tobacco smoke, may affect the genes that govern those proteins, write the researchers.

"It is important to consider wood smoke exposure as a possible risk factor for the development of lung cancer in [nonsmokers]," they write.

Read WebMD's "Secondhand Smoke Hurts Heart Like Smoking"

By Miranda Hitti, reviewed by Brunilda Nazario, MD

SOURCES: Delgado, J. Chest, July 2005; vol 128: pp 124-131. American Cancer Society: "How Many People Get Lung Cancer?" American Cancer Society: "What Causes Lung Cancer?"