Benefits of Aromatase Inhibitors

Aromatase inhibitors have become the standard of care for post-menopausal women with hormone-receptor-positive breast cancer.

Aromatase inhibitors provide many important benefits in various situations. They can:

• reduce the risk of breast cancer coming back,
• reduce the risk of a new breast cancer developing,
• shrink large, hormone-receptor-positive breast cancers before surgery, so you might be able to have a lumpectomy and radiation as opposed to mastectomy, and
• slow the growth of advanced (metastatic) hormone-receptor-positive breast cancer.

Benefits of aromatase inhibitors shown in medical studies

Many large clinical trials have proven the benefits of aromatase inhibitors, all of which have been tested on hundreds and even thousands of women. The three aromatase inhibitors (Arimidex [chemical name: anastrozole], Aromasin [chemical name: exemestane], and Femara [chemical name: letrozole]) are all used for women with advanced (metastatic) disease. Each of the aromatase inhibitors is also used for women with early-stage disease, at different times:

1. Taking aromatase inhibitors after initial treatment with surgery, chemotherapy, and/or radiation:

The ATAC (Arimidex and Tamoxifen Alone or in Combination) study showed that five years of Arimidex was better than five years of tamoxifen as initial hormonal therapy for post-menopausal women with early-stage hormone-receptor-positive breast cancer. Arimidex was shown to be better than tamoxifen for:

• reducing the risk or delaying the cancer coming back in the breast or lymph nodes,
• decreasing the risk of cancer spreading to other parts of the body, and
• lowering the risk of a new breast cancer developing in the other breast.

Women taking Arimidex had fewer mild and serious side effects than women taking tamoxifen. They did, however, have more fractures and joint aches than women taking tamoxifen.

The ATAC trial began in 1999, and the researchers will continue to follow up with the women in the study until 2011.

The BIG (Breast International Group) 1-98 trial showed that five years of Femara was superior to five years of tamoxifen as initial hormonal therapy for post-menopausal women with early-stage hormone-receptor-positive breast cancer. Femara was shown to be better than tamoxifen for:

• reducing the risk or delaying the cancer coming back in the breast or lymph nodes,
• decreasing the risk of cancer spreading to other parts of the body,
• lowering the risk of a new breast cancer developing in the other breast.
• reducing risk for women with more aggressive cancers who had already had chemotherapy or had lymph node involvement.

Women taking Femara had fewer mild and serious side effects than women taking tamoxifen. They did, however, have more fractures and joint aches and higher cholesterol than women taking tamoxifen.

The BIG 1-98 trial began in 2000, and the researchers will continue to follow up with the women in the study until 2008.

2. Switching to aromatase inhibitors after two to three years of tamoxifen:

Switching to Aromasin: The IES Trial (Intergroup Exemestane Study) showed that post-menopausal women with early-stage hormone-receptor-positive breast cancer who switched to Aromasin after two to three years of tamoxifen (for a total of five years) had greater benefits than those who stayed on tamoxifen for five years:

• The women in the group that switched were about one-third less likely than the women who stayed on tamoxifen to have recurrent disease or a new cancer in the other breast.
• There was no significant difference in overall survival between the two groups. Those who switched to Aromasin and those who stayed on tamoxifen lived equally as long.

Switching to Arimidex: A European trial of more than 3,000 post-menopausal women with early-stage hormone-receptor-positive breast cancer showed that it may also be beneficial to switch to Arimidex after two to three years on tamoxifen rather than staying on tamoxifen for five years. Compared to women who stayed on tamoxifen for five years, women who switched to Arimidex after two to three years of tamoxifen:

• had a 40% reduced risk of the cancer coming back in the original breast, and
• had a 40% reduced risk of developing a new cancer in the other breast.

3. Continuing aromatase inhibitors after five years of tamoxifen:

An international study of more than 5,000 post-menopausal women with early-stage hormone-receptor-positive breast cancer showed that it may be beneficial to continue hormonal treatment with Femara after completing five years of tamoxifen. In the study, one group of women took Femara for four years and the other group took a placebo (dummy pill).

• The women taking Femara had fewer recurrences, either local (in the breast area) or distant (beyond the breast and lymph nodes). They also had fewer new breast cancers in the other breast.
• Almost 40% of women with node-positive breast cancer who took Femara after their five years of tamoxifen survived, compared to those who took a placebo.
• For the women with node-negative disease, there was no significant difference in survival between those taking Femara and those taking a placebo.

All these studies add to the growing body of evidence that aromatase inhibitors are an important therapy for women with early-stage disease as well as those with advanced disease. You and your doctor will need to consider all of the factors before deciding on the right hormonal treatment for you.