The growing trend in treating hormone positive breast cancer is to stay on some kind of hormone blocker for a significant period of time. Many women have told me that they fear stopping their tamoxifen or aromatase inhibitor because they think that it is only keeping cells under control, and that without the drugs the cancer will come back.
I always explain that studies have shown that tamoxifen’s benefits lasted well beyond the five years women were on it. It seems like a period of hormone suppression has a long lasting effect, possibly by making any cells that are left dormant inactive or by changing the microenvironment (neighborhood) around the cells so that it keeps the cells in check. Now we’ve got even more data to back that up.
Last month, the Early Breast Cancer Trialists Collaborative Group (EBCTG) reported in the Lancet an updated meta-analysis (a study that combines data from a number of studies) on the long-term benefit of five years of adjuvant tamoxifen.
The meta-analysis included a total of 21,547 women who had taken part in one of the 20 trials in which women were randomized to either tamoxifen or a placebo/observation. (In most of these trials the women took 5 years of tamoxifen, in some the took it for only 2 or 3 years.)
The researchers have been following these women for 15 years so that they could study the long-term effects of tamoxifen. The new analysis showed that during the first four years of tamoxifen use a woman’s risk of recurrence was reduced by 50 percent, and that during years 5 through 9 it was reduced by 30 percent, for an average recurrence rate reduction of 39 percent. (This means that if your chance of recurrence was 10 percent it would be reduced to about 6 percent).
The study found that after five years the absolute mortality difference was only 3 percent (9 percent in the tamoxifen group; 12 percent in the placebo group). By 10 years after stopping the drug (year 15), the absolute mortality difference was 9 percent (24 percent in the tamoxifen group; 33 percent in the placebo group.) In other words it got better over time, even after the drug was stopped.
Most importantly, because the benefit has remained high over the past 13 years, this study tells us that for many women with ER-positive tumors, five years of tamoxifen not only reduces the risk of recurrence but also essentially cures the disease.
These findings should be reassuring to women who were on tamoxifen before the aromatase inhibitors (AIs) were developed. They should also be reassuring to women who switched from an AI to tamoxifen because of some of the common side effects associated with the AIs, like bone and joint pain. And they should be reassuring to premenopausal women for whom tamoxifen has remained the standard of care.
I think that this study may encourage more doctors to prescribe 2-3 years of tamoxifen to all women before they start on five years of an AI. It may also lead to more studies that look at whether five years of tamoxifen would be beneficial after five years of an AI.
These findings also point to the fact that we really don’t fully yet understand how tamoxifen works!