November 6, 1998 (Ira Pilgrim)

Preventing Breast Cancer?

Those responsible for telling the public about cancer have chosen to use the weapon of fear. They have portrayed cancer as an insidious, dreadful, relentless invader. With religious fervor they have fashioned a devil out of cancer. They have bred in a sensitive public a fear that is approaching hysteria. They have created a new disease, cancerophobia, a contagious disease that spreads from mouth to ear. It is possible that today cancerophobia causes more suffering than cancer itself.

George Crile, 1955

Amid great hoopla, the newspeople have told us that there has been a great breakthrough and that breast cancer can now be prevented with a drug called tamoxifen. As a response to this, scads of women are going to ask their doctors to prescribe the drug, so that they will not get cancer. What is it all about?

Some time ago, in trials using tamoxifen to treat incurable breast cancer, medical researchers noticed that women getting the drug had fewer cancers in the breast that did not have the original cancer than those not treated with tamoxifen. Tamoxifen is a drug that blocks estrogen. Based on this observation, a group at the National Cancer Institute and the Allegheny University of the Health Sciences in Pittsburgh decided to test whether tamoxifen could prevent breast cancer in susceptible women; women considered at "high risk" for developing breast cancer. A variety of criteria were used to determine risk including family history, medical history and being over 60 years of age; 39% were age 35-49, 31% were 50-59, and 30% were over 60. The experiment was a double blind one, in which neither the doctors nor the patients knew who was getting the tamoxifen or who was getting the placebo(sugar pill).

The drug was tested on over 13,000 women who were "at high risk" for developing breast cancer. The tests were followed by headlines some six years later, claiming that a drug now exists to prevent breast cancer and that "Tamoxifen reduced the risk of invasive breast cancer by 49%." This was based on a reduction of breast cancer incidence in women taking the drug as compared with women given a placebo(sugar pill). This is not as spectacular as it sounds. What they observed was that, out of every 1,000 women given the placebo, 39 women developed breast cancer in 5 years; while in the tamoxifen-treated group, 19 women developed breast cancer. This might also be called a reduction of 2 to 3 cases per 100 women, or 2 to 3 percent.

Among the side effects of the drug, was cancer of the uterus (endometrial cancer) which developed in 13 out of every 1,000 women getting tamoxifen, compared with 5 per thousand women getting the placebo. This represents an increase of 0.8 cases of uterine cancer per 100 women, or 0.8%. If I wanted to put the same spin on the down side of tamoxifen chemoprevention as its advocates did on the up side, I could say that there was a 160% increase in uterine cancer. Three women given tamoxifen died of blood clots in their lungs, against none in the placebo group. Women getting tamoxifen had fewer bone fractures, indicating that tamoxifen reduced osteoporosis.

At this point, the trials were discontinued.

Does tamoxifen actually prevent breast cancer or, as it does in cancer treatment, just slow down the growth of the cancer so that it did not become evident during the trial? There are two kinds of breast cancer: One type is estrogen sensitive and depriving these tumors of estrogen will slow down their growth or cause some to shrink. These are the cancers that are "prevented" with tamoxifen. The other type is not estrogen sensitive. These tumors are not "prevented" with tamoxifen. This suggests that tamoxifen may not actually "prevent" breast cancer, but slows down its growth and that those cancers might be expected to appear after the tamoxifen treatment is discontinued.

Tamoxifen is a wonderful drug. It has extended the lives of people with incurable breast cancer by many years. Compared to chemotherapy, it has far fewer side effects. However, unlike chemotherapy that can kill cancer cells, it will only inhibit the growth of the cancer. If I had incurable breast cancer, tamoxifen would be my first choice as a drug that could extend my life.

The authors of the study conclude that "Despite side effects from administration of tamoxifen, its use as a breast cancer preventative agent is appropriate in many women at increased risk for the disease." Unfortunately, at the present time, there is no way to identify those women who would actually be benefited. Therefore, out of every 1,000 women at risk, it is necessary to give the drug to 979 women who may not be benefited in order to help 21 women; and to 5 women who might actually be harmed).

If a woman is at high risk for breast cancer; that is if she has one of the so-called breast cancer genes, which goes along with having a number of close relatives who have had breast cancer, she has a number of options. She could be meticulous in breast self examination and hope that she will detect a cancer while it is curable. A second option is mammography. This increases the likelihood of early detection. The down side of this is that women with a breast cancer gene are unusually susceptible to the gene mutation effects of x-ray. Another option is to have her breasts removed. This will reduce the possibility of her ever developing breast cancer by about 98%. It will not be 100% because some breast tissue usually remains. Some women have chosen this option, although most women prefer to keep their breasts and take their chances.

Now tamoxifen offers another option. It is nowhere near as effective as removal of the breasts, and is better than nothing. If I were a woman at high risk, I would consider it. However, breast cancer is easier to detect than uterine cancer and blood clots are very serious, and potentially fatal.

To my mind, the Tamoxifen-Chemoprevention study was the National Cancer Institute's equivalent of the Pentagon's Star Wars program. Now as a result of a statistically significant decrease in the incidence of breast cancer in women taking the drug, it is being touted as a major breakthrough, with all of the attendant hype. I can imagine the drug company that manufactures it planning its advertising campaign.

An honored principle of medical ethics is "First do no harm." To my mind, giving a powerful drug (tamoxifen for the prevention of breast cancer or the statin drugs for the prevention of heart attacks) to healthy people borders on medical malpractice. I am far from alone in this belief.

Next column

Return to the Medicine Home Page

Return to Ira's Home Page