July 24 (HealthDay News) -- Medically induced menopause, particularly when it involves removal of both ovaries, nearly doubles a younger woman's risk for developing lung cancer, a new Canadian study has found.

"It's possible that vulnerability to lung cancer is caused by early and sudden decrease in estrogen levels or potentially long-term use of hormone replacement therapy, and further research is needed to explore these hypotheses," study co-author Jack Siemiatycki, a professor at the University of Montreal's Department of Social and Preventive Medicine, said in a university news release.

The finding, published online in the International Journal of Cancer, is based on a study of 999 patients from hospitals across Montreal, including 422 women with lung cancer. The researchers analyzed the patients' socio-demographic information, place of residency, jobs, medical and smoking history, and (among women) menstruation and pregnancy histories.

"A major strength of this study was the detailed smoking information which we obtained from all study participants," study co-author Anita Koushik said in the news release. "This is important because of the role of smoking in lung cancer and because smokers generally have lower estrogen levels than non-smokers."

"Although smoking is the dominant cause of lung cancer, we know other factors can play an important role in enhancing the impact of tobacco carcinogens," Koushik added. "This research suggests that, in women, hormonal factors may play such a role."

SOURCE: University of Montreal, news release, July 21, 2009