Smoking and Urinary Estrogens

To the Editor: MacMahon and his colleagues have reported that luteal-phase estrogen levels in current smokers were lower than those in nonsmokers (Oct. 21 issue).¹ They suggest that this may explain why women who smoke have an earlier menopause and that cigarette smoking may protect against the development of breast cancer. Of three cited reports that suggest that breast cancer is less frequent in smokers than in nonsmokers, two were prospective studies of breast-cancer mortality in which the differences were not statistically significant,^2,3 and the third was a case–control study in which the authors noted an inverse relation of.