The first scientific observation about breast cancer was made in 1896 when it was noted that the disease sometimes regressed if the ovaries were removed. Eventually this connection was understood in terms of estrogen, the female hormone produced by the ovaries. Some types of breast cancer cells are stimulated to divide by estrogen and therefore blocking this effect constitutes a form of treatment. Many anti-estrogen drugs have been tried with various degrees of effectiveness. Tamoxifen is perhaps the best known of these medications. Prostate cancer cells are also known to be stimulated by hormones, in this case by androgens, the male sex hormones which are produced mostly in the testes. It has long been known that eunuchs do not develop prostate cancer because removal of the testes lowers the level of male hormones in the blood. Indeed, prostate cancer is sometimes treated by surgical removal of the testes. Drugs known as anti-androgens constitute the pharmaceutical treatment of this disease.
