The Surgeon General has concluded that breathing secondhand cigarette smoke causes lung cancer in nonsmokers, largely based on epidemiological studies comparing lung cancer rates in nonsmoking women...

The Surgeon General has concluded that breathing secondhand cigarette smoke causes lung cancer in nonsmokers, largely based on epidemiological studies comparing lung cancer rates in nonsmoking women married to nonsmoking men with those married to smoking men. An alternative approach to seeking risk factors for cancer is to see whether there are differences in the rates of a given cancer in different countries where the exposures to a potential risk factor differ. If the cancer rate varies with the risk factor across different countries, then the data suggest that the risk factor causes the cancer. This is the approach we used in to relate sperm damage to cell phone exposure. To investigate whether or not involuntary smoking was associated with breast cancer, Horton † collected data on female breast cancer and male lung cancer rates in 36 countries (the data are in Table D-2, Appendix D). Because, on a population basis, virtually all lung cancer is due to smoking, Horton took the male lung cancer rate as a measure of exposure of women to secondhand tobacco smoke. Is female breast cancer associated with male lung cancer rates? In other words, is there evidence that breathing secondhand tobacco smoke causes breast cancer?

Table D-2