From the PCRM website (

Soy consumption may help fight lung cancer, according to a new study. Researchers in the Japan Public Health Center-based Prospective Study looked at 76,661 participants’ lifestyle factors and lung cancer risk and found that those who consumed the most soy had the lowest risk of lung cancer. Among men who never smoked, researchers saw a significantly lower risk of lung cancer in those who consumed the most soy, compared with those who consumed the least. Researchers saw similar results in nonsmoking women, but they could not rule out statistical chance as the reason for these results. People who consumed the most soy may have also participated in other activities that could lower risk such as eating more fruits and vegetables. Soy foods in this study included miso soup, soymilk, a variety of tofu dishes, and fermented soybeans.

Schimazu T, Inoue M, Sasazuki S, et al. Isoflavone intake and risk of lung cancer: a prospective cohort study in Japan. Am J Clin Nutr. Published ahead of print January 13, 2010. doi:10.3945/ajcn.2009.28161.