Do We Know the Causes of Breast Cancer?

The causes of cancer are, generally, neither well known nor well understood. For a few types of cancer, however, we have evidence concerning risk factors and even causative factors. For example, 90 percent of lung cancer cases are associated with cigarette smoking, establishing a cause-and-effect relationship. Indeed, until the mass consumption of cigarettes began just after World War I, lung cancer was very uncommon. We should now be able to virtually prevent lung cancer by urging smokers to quit, or, better yet, educating them so they do not start smoking in the first place.

But this is not the case with breast cancer. We know very little of practical value — with a few promising exceptions — on how to prevent this disease.

We do know, for example, that women who began menstruating earlier in life (before age 12) and those who enter menopause later in life (after age 55) have a statistically increased risk of developing breast cancer. Similarly, we know that women who have no children or those who have a first child after age 30 or 35 have a somewhat increased risk of developing breast cancer — early pregnancy seems to convey some protection. Further, there is evidence that after menopause, obesity contributes to a woman’s risk of breast cancer. The use of estrogen replacement therapy also seems to increase the risk slightly, although in most cases that risk is outweighed by the overall health benefits.

The media, however, often reports the calls of those who claim that exposure to trace levels of environmental chemicals, such as DDT and PCB, cause breast cancer. There is no evidence that this is the case. Similarly, for more than two decades there have been those who maintained that diet is an important factor in the causation of breast cancer. But according to a recent issue of the American Cancer Society Journal CA: A Journal for Clinicians, “current info don’t support specific dietary recommendations for decreasing breast cancer risk.”

On a related subject: While it has long been hypothesized that alcohol is a risk factor for breast cancer, there is, according to CA, no solid evidence here as well. In the case of both alcohol and diet, however, women would be well advised for general health reasons to adopt a moderate, varied low-fat diet and consume alcohol in moderation if they choose to drink.

Clearly, having a mastectomy to prevent cancer is a drastic measure, with both physical and psychological effects. But the future is promising for chemoprevention generic drugs such as tamoxifen and a related drug called raloxifene. The former has been proven to reduce cancer frequency in high-risk women; the latter is now under study.

The bottom line is that the best hope for breast cancer prevention lies not in the avoidance of hypothetical risks — such as trace chemicals in the environment — as a cause of breast cancer, but rather in turning to the scientific evaluation of chemopreventive pharmaceuticals, particularly for high-risk women.

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