June 3, 2014 | by Hiu Chung So
For premenopausal, hormone-sensitive breast cancer patients, the estrogen blocker tamoxifen is often prescribed after surgery to help prevent the cancer from returning. But new research data may change this longstanding practice since it found the aromatase inhibitor exemestane (trade name Aromasin) to be more effective this role.
These findings came from a joint analysis of two phase III breast cancer clinical trials, called TEXT and SOFT, and were presented during the plenary session of the American Society of Clinical Oncology annual meeting.
Reporting on the study, lead author Olivia Pagani, M.D., said that the exemestane group were 34 percent less likely than the tamoxifen group to develop a subsequent breast cancer.
"For years, tamoxifen has been the standard hormone therapy for preventing breast cancer recurrences in young women with hormone-sensitive disease. These results confirm that exemestane with ovarian function suppression constitutes a valid alternative," said Pagani, clinical director of the Breast Unit at the Oncology Institute of Southern Switzerland, in a press release.
For this study, Pagani and her team looked at data from almost 4,700 women in both trials. The women had all undergone initial breast cancer surgery and were then randomized to receive five years of either tamoxifen or exemestane. Additionally, all women were given ovarian function suppression therapy, which can include oophorectomy (surgical removal of the ovaries), ovarian irradiation or drugs that stop the ovaries from working.
After follow-up and analysis, the researchers found that breast cancer-free survival was 88.8 percent in the tamoxifen group and 92.8 percent in the exemestane group. Significant improvements were also seen in overall cancer-free survival (87.3 percent in tamoxifen, 91.1 percent in exemestane).
"There is another large clinical trial comparing tamoxifen to anastrazole — another aromatase inhibitor — and patients in the anastrazole group actually did worse," said Mortimer, who is not involved in the TEXT/SOFT studies.
In that trial, whose results are published in The Lancet, women on anastrazole (trade name Arimidex) therapy had lower overall survival compared to the tamoxifen group. Pagani said she currently does not have enough data to examine for differences in overall survival, which compares likelihood of dying as opposed to cancer recurrence.
Further, the plenary discussion yielded additional considerations, such as cost (exemestane is currently a patented brand name drug and thus considerably more expensive than the generic tamoxifen) and quality-of-life concerns (Pagani's abstract showed that the exemestane group had more serious and life-threatening side effects than the tamoxifen group.)
Given these contradictory findings, Mortimer said there should be further studies and discussion comparing tamoxifen to aromatase inhibitors before changing clinical guidelines for postsurgery hormone therapy.
For now, women with hormone-sensitive breast cancer should consult with their oncologists to determine the best treatment option to help prevent recurrence and maintain quality of life.
This study's abstract (LBA1) is available online on ASCO's website.
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