Research presentations at this year's San Antonio Breast Cancer Symposium, held December 4 - 8, included some promising leads for improved treatment of estrogen receptor-positive, HER2-positive, and triple-negative breast cancer. One report, in particular, promises to change our practice almost immediately.
Ironically, the change involves one of the oldest breast cancer medications, tamoxifen. Leaders of the ATLAS trial, which involved thousands of breast cancer patients worldwide, reported that patients with estrogen receptor-positive breast cancer who took tamoxifen for 10 years had a higher survival rate and lower chance of recurrence than those who took the medication for five years.
Interestingly, the biggest benefit appeared to accrue after women finished the 10-year course of therapy. That is, although the benefits began to be apparent during the five additional years that one group took tamoxifen, the advantages became even greater after the 10-year group went off-therapy.
At the Breast Oncology Center at Dana-Farber, we generally don't use tamoxifen as the only treatment for post-menopausal women with breast cancer; we either replace tamoxifen with aromatase inhibitors or use a sequential approach of tamoxifen followed by an aromatase inhibitor. For such patients, the results of the new study aren't likely to change our practice, except to the extent that we have a clearer picture of the benefits of prolonged endocrine therapy. We're eager to see the results of ongoing studies of the effect of extending aromatase inhibitor therapy beyond five years in post-menopausal women.
In pre-menopausal women – particularly those women who were pre-menopausal both at diagnosis and at completion of tamoxifen therapy – the study suggests that the new standard of care is 10 years of tamoxifen, unless they have severe side effects to the medication or have a very low risk of recurrence.
The study found that extended tamoxifen use was associated with a 1.6 percent increase in endometrial cancer risk. Most of that risk, we know from previous studies, pertains to post-menopausal women. Since the number of deaths from endometrial cancer is very small, the benefits of extended therapy still outweigh the risks for most patients.
Although the number of practice-changing studies presented at San Antonio this year was small, there were a great many studies whose impact on clinical practice is only a few years off. It remains a very exciting time in breast cancer research.
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