Two separate meta-analyses of clinical trials from around the world that tested tamoxifen against aromatase inhibitor drugs in postmenopausal women with early breast cancer have each reached the same conclusion: aromatase inhibitors are more effective in preventing breast cancer from coming back.
Patients using aromatase inhibitors had more than a 3 percent lower cancer recurrence 6-8 years after diagnosis, compared to women using tamoxifen alone.
One of these studies also found a significant survival benefit (1.6 percent) for users of aromatase inhibitors, but researchers say not enough time has passed since treatment to judge with confidence whether one drug is superior to another in saving lives. The joint analyses are being presented at the Cancer Therapy & Research Center-American Association for Cancer Research (CTRC-AACR) 31st annual San Antonio Breast Cancer Symposium. "Tamoxifen is a good drug, but it looks like aromatase inhibitors may be somewhat better," says James Ingle, M.D., a professor of oncology at Mayo Clinic, who is presenting the results on behalf of the Aromatase Inhibitors Overview Group (AIOG).
"The importance of these findings can be seen from the fact that 80,000 to 90,000 women in the United States alone are using endocrine therapy this year," he says. "While a three percent difference in cancer recurrence may not seem like much, it can mean that several thousand women could be spared from a breast cancer recurrence."
This international group includes leaders of all the major clinical trials that tested aromatase inhibitors against use of tamoxifen. AIOG is a subset of the Early Breast Cancer Trials Collaborative Group (EBCTCG), a global organization of researchers that studies all randomized evidence of therapies used to treat breast cancer to find insights not apparent from examining individual trials - a technique known as a meta-analysis. The AIOG collaboration is led by Professor Mitch Dowsett of the Royal Marsden Hospital, London, UK.
Tamoxifen and aromatase inhibitors are widely used to prevent recurrence of, or to treat, tumors that are estrogen-receptor positive (ER+), which comprise 70 to 80 percent of all breast cancers.
While individual studies of tamoxifen and aromatase inhibitor drugs (including anastrozole, exemestane and letrozole) have found benefit for aromatase inhibitors, it was critically important that data from all of these studies be pooled and examined, Professor Dowsett says. "This kind of analysis provides knowledge on such end points as survival and allows us to have confidence that the improvement in preventing the return of breast cancer applies to all subgroups of patients but that those at greatest risk of recurrence have most to gain. That is not possible even with a large individual trial," he says. "The global community has come together to do this."