A recent study concluded that the risk of breast cancer is significantly increased in women who had ever been pregnant and who started to smoke within five years of their first menstrual period. Risk was also increased in never-pregnant women who smoked 20 cigarettes daily or more over a period of twenty years. The results are based on a questionnaire sent to 1431 women under the age of 75 who had been diagnosed with breast cancer, as compared to an age-matched cancer-free control group. The deleterious effect of chemical carcinogens on breast tissue has long been suspected but this study confirms some of the worst suspicions. The impact of smoking on developing breasts is particularly noteworthy and hopefully may lead to increased efforts to discourage adolescent girls from taking up the habit. (Band, P.R., Le, N.D., Fang, R., Deschamps, M. Carcinogenic and endocrine disrupting effects of cigarette smoke and risk of breast cancer. The Lancet 360 (9339): 1044-49, Oct. 5, 2002)

Women whose mothers took DES may have an increased risk of developing breast cancer, according to a new study. The researchers are following a cohort of 4821 women exposed to DES in utero over the last 19 years, and comparing them to a control group of 2095 unexposed women. The incidence of invasive breast cancer in the DES group is 40% higher, specifically among DES daughters aged 40 and older. Moreover, nearly all cases of breast cancer in this group were characterized by estrogen receptor positive tumours. Given the difficulty of establishing whether a mother was actually administered DES to prevent miscarriage in the years between 1941 and 1971 (when DES was withdrawn from the market), it may be difficult for a DES daughter to establish her status with certainty, and to know whether other hormonal medications — prescribed to counteract infertility, osteoporosis, or other conditions — may increase her risk of developing breast cancer. (Palmer, J.R., Hatch, E.E., Rosenberg C. L., et al. Risk of breast cancer in women exposed to diethylstilbestrol in utero: Preliminary results. Cancer Causes and Controls, October 2002)