Indoor tobacco smoke pollution. A major risk factor for both breast and lung cancer?

Among 51 countries, those having high mortality rates for male lung cancer generally have high rates for female breast cancer (highest in England, Scotland, and the Netherlands). Conversely, those having low rates for one disease have low rates for both (P less than 0.001). Mortality rates available for 23 of the countries for 1954, 1964, and 1974 show a constant relationship of the female breast cancer rate, y = 13.3 + 0.17x (where x is the male lung cancer rate). Where data on 1950 tobacco consumption are available (20 countries), an even closer relationship with female breast cancer mortality in 1974 is observed. Because women in many of these countries account for only a small fraction of the tobacco consumption, the conclusion is that the risk of the female disease is closely related to the extent of male smoking. Thus, breast cancer is apparently initiated by the involuntary inhalation of indoor tobacco smoke for more than two decades on the average before diagnosis. The same relationship between female breast and male lung cancer is found in incidence rates for 80 populations of five continents, including northern and western populations of the US. Trends in age-adjusted breast cancer incidence rates rose almost 50% in many of these populations from 1950 to 1975. This increase corresponds to a tripling of cigarette consumption in the US from 1927 to 1952. There is a strong need to analyze passive smoking more than two decades before diagnosis as a confounding variable in all studies of other risk factors for breast cancer such as alcohol, dietary fat, and endogenous or exogenous estrogen. Comparison of incidence rates for lung cancer and lifetime cigarette consumption in various cultures of Hawaii indicates that even for male smokers, additional exposure to high levels of indoor tobacco smoke greatly increases their risk of lung cancer. This brings the safety of designated smoking areas into serious question.