How Long is Too Long on Tamoxifen?

Recommendations Evolve, and So Do Fears

The ideal duration of anti-estrogen/hormonal therapies for women who have ER positive breast cancer seems to be a moving target. For a long time, women who had been pre-menopausal at the time of diagnosis were prescribed tamoxifen for five years. Women who were post-menopausal at diagnosis were given one of the AIs for the same length of time.

Over the past 10 years or so, that has evolved and changed. For a relatively brief period, the standard for younger women was two or three years of tamoxifen and then a switch to one of the AIs for a total of five years. Then there began to be studies suggesting that keeping women on these therapies for longer reduced recurrences and extended survival. Many women were told to stay on the medicines for seven years or ten years or longer. The suggested total time is variable woman to woman and completely dependent upon both the specifics of her breast cancer and any side effects she may be experiencing from the drugs. There are clinical trials that combine injections to shut down ovarian function with AIs for younger women. 

Sometimes referred to as the work horse for women with ER positive breast cancers, these hormonal therapies are extremely important and effective. Like any drugs, however, they come with some possible side effects. For the AIs, the biggest concern is bone density, and women are usually advised to have a bone density test at the start and then repeat tests every two or so years.  Many women also experience joint aches and pains that can range from a little stiff to very uncomfortable. With tamoxifen, the biggest risks are endometrial cancer and blood clots. This sounds very scary, but the risks are quite small. In all my years of practice, I have known only one woman who had a blood clot (and that was successfully treated) and no one who developed endometrial cancer.

A recent study published in the British Journal of Medicine indicated clear evidence that 10 years of tamoxifen therapy does reduce local recurrence and improve breast cancer-free survival. However, it also reported that extended use (10 years rather than five) was linked with a two-fold increase in endometrial cancer. The recommendation was that women continuing on tamoxifen should be screened for endometrial cancer; this usually means a vaginal ultrasound. The risk of developing this second cancer is still very low, but this finding does highlight the ongoing balance between risk and benefit.

In my groups as well as in individual sessions, there is often conversation about how long to stay on these drugs. Nationally, there is a reported problem with compliance; that is, many women do not take the drugs as prescribed. The reasons given are related both to cost and to side effects. Honestly, I don’t hear much about this. More often, I listen to women who are afraid to stop the pills that they believe are keeping them healthy. There is a lot of discussion about how to talk with their doctors about staying on the drug for more than 10 years. There are, of course, some women who can't wait to stop the medication, who would strongly resist any suggestions that they continue past the anticipated stop date.

For some women, that is exactly what the doctor will suggest. For others, the recommendation will be to stop after a specific period. Like everything else related to cancer, this is a gray area, and the best and only advice is to talk with your doctor about your particular situation. The equation will have to include any other medical problems, the presence of side effects, quality of life, and, of course, the specifics of your breast cancer.