A study found that taking the aromatase inhibitor Femara (chemical name: letrozole) after taking tamoxifen for 5 years reduced the risk of the breast cancer coming back (recurrence), compared to not taking Femara after tamoxifen. These results were significant, which means they likely happened because of the Femara and not just by chance.
The risk of the cancer coming back was lowered by 63% in women who started taking Femara up to 7 years after finishing 5 years of tamoxifen. The women took Femara for 5 years.
Hormonal therapy, with either tamoxifen or an aromatase inhibitor, is usually taken for 5 years after surgery (and possibly radiation and chemotherapy) to lower the risk of hormone-receptor-positive early-stage cancer coming back in postmenopausal women. But the risk of the breast cancer coming back doesn't end after these 5 years of hormonal therapy. (This 5-year schedule was created because taking tamoxifen longer than 5 years doesn't offer any additional benefits.)
Tamoxifen works by blocking the effects of estrogen on breast cancer cells. Aromatase inhibitors help stop breast cancer from coming back by preventing the formation of estrogen. Because these two types of hormonal therapy medicines work differently, researchers wondered if taking aromatase inhibitors after 5 years of tamoxifen, for a total of 10 years of hormonal therapy, would offer additional risk reduction benefits. This study confirms earlier results showing that 10 years of hormonal therapy, first with tamoxifen, then with an aromatase inhibitor, continues to reduce the risk of the cancer coming back.
About 5% of the women who took only tamoxifen for 5 years had the cancer come back during the 3 years after the research ended. Only 2% percent of the women who took tamoxifen for 5 years and then took Femara for 5 years (for a total of 10 years of hormonal therapy) had the cancer come back.
When this study was started, tamoxifen was the hormonal therapy used to reduce the risk of hormone-receptor-positive early-stage breast cancer coming back in postmenopausal women. Since that time, aromatase inhibitors have been found to work a little better than tamoxifen to reduce the risk of recurrence. Besides Femara, there are two other aromatase inhibitors: Arimidex (chemical name: anastrozole) and Aromasin (chemical name: exemestane).
This study looked at Femara, but it's likely that all of the aromatase inhibitors can reduce the risk of the cancer coming back when taken after 5 years of tamoxifen.
If you're finishing 5 years of tamoxifen, talk to your doctor about the pros and cons of taking an aromatase inhibitor for another 5 years to continue to reduce your risk of the cancer coming back. Together, you and your doctor can decide on an approach that is right for YOU and your unique situation.