Exposure to Wood Smoke May Increase Lung Cancer Risk
Laurie Barclay, MD;
Medscape Medical News 2005. © 2005 Medscape
July 11, 2005 Exposure to wood smoke may increase the risk of lung cancer via a mechanism similar to that of tobacco, according to the results of a study published in the July issue of Chest .
"... our findings demonstrate that wood smoke could produce similar effects on p53, phospho-p53, and MDM2 protein expression as tobacco. It is important to consider wood smoke exposure as a possible risk factor for the development of lung cancer in nonsmoker subjects."
"Tobacco is considered the most important cause of lung cancer, but other factors could also be involved in its pathogenesis," write Javier Delgado, MSc, from Instituto Nacional de Enfermedades Respiratorias in Calzada de Tlalpan, Mexico, and colleagues. "The aim of the present work was to establish an association between wood smoke exposure and lung cancer pathogenesis, and to analyze the effects of wood smoke on p53 and murine double minute 2 (MDM2) protein expression."
The investigators studied blood samples from 62 patients with lung cancer, nine with chronic obstructive pulmonary disease (COPD), and nine control subjects. Of the 62 patients with lung cancer, 23 (37.1%) were tobacco smokers, 24 (38.7%) were exposed to wood smoke, and 15 (24.2%) did not smoke tobacco and were not exposed to wood smoke. Western blot analysis detected p53, phospho-p53, and MDM2 isoforms in plasma samples, and densitometric analysis determined the intensity of p53, phospho-p53, and MDM2 bands.
Most of the lung cancer patients with wood smoke exposure were women living in rural areas; 46.7% had adenocarcinoma. Compared with the other groups, lung cancer patients with wood smoke exposure had significantly increased p53 and phospho-p53 proteins (56,536.8 ± 4,629 densitometry units [DU], and 58,244.8 ± 7,492 DU, respectively). The 57-kD MDM2 isoform plasma concentration was very high in this group (75,696.4 ± 11,979 DU) and in the lung cancer patients who smoked (78,551.7 ± 11,548 DU).
Control subjects and those with COPD had high concentrations of MDM2-p53 complexes allowing p53 degradation, which explains the low concentrations of p53 in these groups. Only subjects with COPD had MDM2-phospho-p53 complexes, which correlates with the low concentration of p53 in this group (13,657 ± 2,012 DU). This may also explain the different clinical course in these smokers compared with those who developed lung cancer.
"This study suggests that there is a possible association of lung cancer with wood smoke exposure," the authors write. "Likewise, our findings demonstrate that wood smoke could produce similar effects on p53, phospho-p53, and MDM2 protein expression as tobacco. It is important to consider wood smoke exposure as a possible risk factor for the development of lung cancer in nonsmoker subjects."
Chest . 2005;128:124-131
Reviewed by Gary D. Vogin, MD
NEW YORK (Reuters Health) - Although tobacco smoke is the top cause of lung cancer, some cases of the disease can be traced to smoke of a different sort, according to a new study.
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.