Cigarette smoking and breast cancer risk.

Luo et al. have had the advantage of assessing active and passive smoking effects on breast cancer in 40 clinical centers in the USA involving 79,990 women aged 50-79 years, who were enrolled in the Women's Health Initiative Observational Study from 1993 to 1998. This is the possibly the largest cohort that has demonstrated the hazards of cigarette smoking and its impact on carcinoma of the breast in women.