Breast cancer strikes men at a rate one-hundredth that of women, but men who work around gasoline and combustion products have a significantly higher risk of developing the disease. Researchers found that men who had been exposed to gasoline and combustion products for at least 3 months were more than twice as likely to develop breast cancer as those who had not been exposed. In addition, men who began working in these trades before age 40 were almost four times as likely to develop the disease.
American Journal of Industrial Medicine 2000;37:349-352
Gasoline, and any other petrochemical solvent or pesticide, will increase breast cancer in men OR women. Some researchers believe the mechanism involves stimulation of certain enzyme systems in the liver. When one is exposed to these toxic chemicals the body attempts to eliminate them. The major way it does this is through the liver. However, it must do this by increasing certain enzyme systems (cytochrome P-450 enzymes) to break these chemicals down. When these enzymes are stimulated they don't just stop breaking down the gasoline or pesticides. They actually start to metabolize some of the body's own hormones as, chemically, they are very similar to gasoline. The danger occurs when it starts to break down estrogen. The estrogen breakdown products are highly cancerous.
This is the main reason that breast cancer is much more common in women, as they have very high estrogen levels to begin with. So, breast cancer appears to be related to two factors, high pesticide exposure and high estrogen levels. This is one of the reasons why it is nearly always unwise for women to be placed on any estrogen. It is also a major reason why one should consume organic food as frequently as possible.