Says Russo, “The fact that carcinogen-metabolizing enzymes such as CYP1A1 are increased in both lung and breast cancers, but that the death rate from lung cancer in American women has increased six hundred percent from 1930 to 1997, whereas breast cancer has remained stationary during the same period, might suggest that women carriers of susceptibility genes would be more prone to develop both breast and lung cancer. This evidence concerns the gene CYP1A1 and lung cancer.