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Aromatase inhibitors can prevent breast cancer better than Tamoxifen in postmenopausal women

Two separate meta-analyses of clinical trials that tested Tamoxifen ( Nolvadex ) against aromatase inhibitors 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 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.
The analyses were carried out by 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.

Tamoxifen and aromatase inhibitors are widely used to prevent recurrence of, or to treat, cancers that are estrogen-receptor positive ( ER+ ), which comprise 70 to 80 percent of all breast tumors.

While individual studies of Tamoxifen and aromatase inhibitor drugs [ including Anastrozole ( Arimidex ), Exemestane ( Aromasin ) and Letrozole ( Femara ) ] have found benefit for aromatase inhibitors, it was critically important that data from all of these studies be pooled and examined.

The Researchers divided the major studies into two different cohorts, or groupings. Cohort 1 consists of clinical trials in which patients were randomized to treatment with either Tamoxifen or aromatase inhibitors for five years. Two trials were examined ( ATAC and BIG 1-98 ) that included 9,856 patients. Cohort 2 included studies in which breast cancer patients received Tamoxifen for two to three years and then were randomized to complete their five years of adjuvant endocrine therapy with Tamoxifen or to receive an aromatase inhibitor for the remainder of their five years of therapy. These studies ( ABCSG 8, ARNO 95, IES/BIG 2-97, ITA ) enrolled 9,015 patients.

The AIOG Researchers found that in cohort 1, five years after beginning treatment, women using aromatase inhibitors had a 2.9 percent lower recurrence rate than those women who received Tamoxifen; that decrease in recurrence rate increased to 3.9 percent at eight years after diagnosis. There were no statistically significant gains in survival between the two groups.

In cohort 2, six years after the randomization, there was a 3.5 percent reduced risk of breast cancer recurrence in women who switched to aromatase inhibitors, compared to women who continued using Tamoxifen. There was also a 1.6 percent reduced risk that patients using aromatase inhibitors would die from their disease, a statistically significant difference. ( Xagena )

Source: Mayo Clinic, 2008