Ten years of anti-estrogen treatment with tamoxifen appears to be better than the more standard 5 years in reducing the risk for breast cancer recurrence and death due to the disease. A trial conducted in the United Kingdom (aTTom, of adjuvant Tamoxifen Treatment offers more?) confirms the results from another international trial, the ATLAS (Adjuvant Tamoxifen, Longer Against Shorter). We saw the ALTAS results in late 2012. Now comes this new study, in which nearly 7,000 women received 5 years of tamoxifen and were then randomly assigned to either stop treatment or continue treatment to 10 years. The longer treatment group had fewer breast cancer recurrences (28% versus 32%), compared to the shorter use group. The risk of death dropped from 24% to 21% as well.
So what’s the downside? Well, there was an increase in endometrial (uterus) cancer in the long-term use group. In the longer treatment group, 1.1% died of endometrial cancer, compared to 0.6% in the shorter use group. Still, it is estimated that for every endometrial cancer death that occurs as a side of effect of long-term tamoxifen, there would be 30 deaths from breast cancer prevented. In addition, many women experience side effects such as hot flashes (and less commonly, vaginal discharge and dryness; joint pain). Perhaps not surprisingly, only 75% were continuing to take their tamoxifen as prescribed by the end of the study.
Who needs to pay close attention to these results? Premenopausal women with hormone receptor positive breast cancer might be the key group. In conclusion, while daily tamoxifen for 5years if the current worldwide standard for the treatment of hormone receptor-positve breast cancer (and reduces the risk of death), we now know that extending treatment beyond 5 years has benefits (that appear to outweigh the risks for most women). We often switch away from tamoxifen (to an aromatase inhibitor drug) for women who past menopause.