Mismo journal que el estudio que posteaste, científicos de la misma universidad del estudio que posteaste, solo que dos años más reciente:
Fifteen percent of lifetime smokers develop lung cancer, but 10% of lung cancers occur in never-smokers (5). In nonsmokers, exposure to secondhand smoke or to other lung carcinogens, such as radon or asbestos, may be contributory. Recent studies suggest that high-dose vitamin E supplementation (6), indoor air pollution from solid fuel use (7), and cannabis smoking are similarly associated with increased risk for lung cancer. Each cannabis cigarette was equivalent to 20 tobacco cigarettes in risk of lung cancer (8).
Update in Lung Cancer 2008