Estrogen and Breast Cancer.

The amount of estrogen a woman produces throughout her life is correlated with her risk of breast cancer. This is why women who bear many children at a young age have a lower risk of breast cancer than those who never have children or those who have a small family later in life. (If you're pregnant or lactating, you aren't producing as much estrogen.) Some recent studies have explored this connection:

* A study published in the 2/27/97 issue of the New England Journal of Medicine discovered that older women with strong healthy bones run a sharply higher risk (almost four times higher than those with the weakest bones) of breast cancer. Having strong bones is ordinarily thought to be a good thing, enabling women to avoid osteoporosis and hip fractures. But healthy bones also reflect a high lifetime exposure to estrogen.

A bone density test costs about $100. The findings can be combined with other known risk factors -- family history, alcohol consumption, and reproductive history -- to help single out women who are at especially high risk.

These findings do not mean that women should not try to keep their bones healthy, since exercise and calcium can also increase bone strength and do not lead to an increased cancer risk The findings also offer no evidence for or against giving estrogen supplements after menopause, since the bone density in his study largely resulted from the women's estrogen levels during their reproductive years.

* High concentrations of estrogen circulating in a woman's womb may increase her daughter's subsequent risk of getting breast cancer. Researchers already knew that women with higher-than-average concentrations of estrogen in their blood during pregnancy gave birth to heavier babies. Several studies have now found that heavier babies have a greater chance of later developing breast cancer. The 12/7/96 issue of The Lancet published a study that found the risk of cancer for women who weighed 5.5 pounds or less at birth was less than half the risk faced by women who had tipped the delivery scales at more than eight pounds. And the 1/1/97 issue of the Journal of the National Cancer Institute details a study from Sweden comparing 1,068 women who had developed breast cancer with 2,727 women of the same age who did not get this cancer. They found a sharply reduced risk of breast cancer among women whose mothers had developed toxemia. Such women showed nearly a 60 percent decreased risk of breast cancer risk. One of the correlates of toxemia is a lower amount of estrogen circulating in the blood.

* Many chemicals of the 20th century, such as pesticides and some PCBs, have estrogenic effects on the body. Many researchers think that the prevalence of these chemicals in our environment is one of the reasons breast cancer has reached epidemic proportions. Tamoxifen, a medication given to many breast cancer patients, has anti-estrogenic properties.

Some scientists have pointed out that the estrogenic activity of environmental chemicals is usually very small when compared with that of DES and hence of little biologic importance. But a study published in the 7/7/96 issue of Science found that chemicals that had little or no detectable estrogenic activity when studied singly could have a 160- to 1600-fold increase in strength when tested in combination.