Although tobacco smoke is the top cause of lung cancer, some cases of the disease can be traced to smoke of a different sort, a new study suggests.

Researchers in Mexico found that of 62 lung cancer patients they assessed, more than one-third of the cases were associated with exposure to wood smoke. These patients, mainly women, were non-smokers who for years had used traditional wood-burning stoves that were not equipped with a chimney to funnel the smoke outdoors.

In many countries, wood and other solid fuels are still used for heating and cooking, and some studies have found potential health hazards. A study in Brazil showed that wood-burning stoves may raise the risk of mouth and throat cancers, while others have found that smoke from wood and other sources may contribute to chronic bronchitis, emphysema and Asthma.

There has not, however, been sufficient evidence to tie wood smoke to lung cancer, according to the authors of the new study, led by Javier Delgado of the National Institute of Respiratory Diseases in Calzada de Tlalpan, Mexico.

Their study, published in the medical journal Chest, included 62 patients scheduled to undergo chemotherapy for lung cancer, as well as nine smokers with Chronic obstructive pulmonary disease and nine healthy non-smokers with no exposure to wood smoke.

Overall, 39 percent of the lung cancer cases were associated with wood smoke, while 37 percent were linked to tobacco smoking. The rest could not be clearly tied to either.

An analysis of tumor samples from some patients showed that both wood smoke and tobacco smoke seemed to cause similar molecular changes. Patients in both groups showed, for example, increased activity in the tumor-suppressing p53 gene, the gene that is most commonly mutated in cancer.

“Our findings,” Delgado and his colleagues write, “suggest that wood smoke, like tobacco smoke, could be involved in lung cancer (development).”

It’s important, they add, to consider wood smoke exposure as a possible risk factor for the disease in non-smokers.

Of the 24 study patients with cancer associated with wood smoke, 22 were women living in rural, impoverished areas.

“In our country, women are exposed to wood smoke for many hours per day,” the study authors note. “That could explain the higher incidence of lung cancer associated with wood smoke in women.”

SOURCE: Chest, July 2005.