A drug that can cut a woman’s risk of breast cancer in half when taken regularly is proving to be a tough sell when women have a chance to fully understand the pros and cons of the medication.
The drug is tamoxifen. For women at high risk of breast cancer (who have a gene associated with it or a close relative with breast cancer), tamoxifen can reduce the odds of developing breast cancer by 50 percent. Yet recent studies show that when the statistics are laid out for women to make an informed choice, only one in 100 actually fill the prescription.
Are the women who decline to take tamoxifen being illogical? Or just making their own personal choices about what is important to them?
Tamoxifen interferes with the body’s use of estrogen. That can lower the risk of estrogen-dependent breast cancers but can increase the risk of other estrogen-related side effects like cancer of the endometrium (the lining of the uterus), blood clots and sexual dysfunction.
Here is how the numbers were spelled out to women in a recent study at the University of Michigan, as reported by Tara Parker Pope in the New York Times:
The risks of breast cancer vary with age, family history, and age of first childbirth. So a 52-year-old woman who had her first baby after age 30 and whose mother had breast cancer, has about a 1.9% risk of developing breast cancer over the next five years. If 1,000 women just like this 52-year-old took tamoxifen over those five years, the research says that here is what would happen:
* Of the nineteen women (same as 1.9%) who otherwise would have developed breast cancer, nine will not develop breast cancer. (Thus the statistic about lowering the odds by half.)
* Thirteen women would avoid broken bones from osteoporosis, another benefit of tamoxifen.
* Twenty-one women would develop endometrial cancer (typically more treatable and less deadly than breast cancer if caught early).
* Twenty-one women would develop blood clots.
* Thirty-one women would develop cataracts.
* Twelve women would experience sexual problems.
* One hundred twenty extra women would get hot flashes and other menopausal symptoms (in addition to those who would get such symptoms anyway).
Behavioral economists might say this is an example of “omission bias,” where we are more worried about a small risk from doing something new (taking a pill) than we worry about a larger risk from doing nothing. Put another way, we often see the status quo of doing nothing as safer when it really isn’t.
At least that’s how the researchers quoted in the NYT article explained the unpopularity of tamoxifen. But for readers who posted comments on the newspaper’s blog, they tended to see the women voting against tamoxifen as being quite sensible. It just doesn’t sound worth the downside.
Part of the problem is the apples-to-oranges comparisons involved when a fatal condition is compared to a non-fatal one. As one commenter posted:
What might make women make better choices is if they had data on whether the pill reduced the risk of DEATH from all causes. If only some of the breast cancers avoided would have resulted in death but all of the endometrial cancers aquired resulted in death, women might make the choice to avoid tamoxifen. If the risks were reversed, they might choose to take tamoxifen. We have to move beyond a discussion of risk of cancer and towards a discussion of risk of cancer DEATH.
http://www.medpie.com – Barbara Lock, MD
If we had the same careful discussion about mammograms, women likely would opt for far fewer of these tests, which save lives on a similar scale as tamoxifen, with plenty of downside.
My conclusions from this debate:
* Patients need to know there are no magic bullet drugs that are all gain, no pain. Tamoxifen interferes with estrogen, which is good for some diseases, not so good for others. This is typical. Each drug must be carefully weighed for its pros and cons.
* We’re all better off with a full exploration of the odds and then make our own decisions. There is no right or wrong.
* The best way to understand risk is the way it’s spelled out here: with numbers of actual people in a given standard-sized group. It’s too confusing when we talk about percent this and percent that.
I tell readers how to do this technique of “counting the people” in my book: The Life You Save: Nine Steps to Finding the Best Medical Care — and Avoiding the Worst.