Evidence Supporting a Switch to Aromasin® Following 2 to 3 Years of Tamoxifen
According to an article recently published in the Lancet, postmenopausal women with hormone-positive breast cancer achieve improved cancer-free and overall survival if they switch to the aromatase agent Aromasin® (exemestane) after two to three years of treatment with tamoxifen (Nolvadex®).
A majority of breast cancers are estrogen receptor-positive (ER-positive), which often referred to as hormone positive. This means that the cancer is stimulated to grow by the female hormones estrogen and/or progesterone. Depriving hormone-positive breast cancers of estrogen can slow the growth of these cancers. Patients with hormone-positive breast cancer are often treated with therapy referred to as hormone therapy.
For many years tamoxifen has been a mainstay of hormonal therapy for breast cancer. Tamoxifen acts by blocking estrogen receptors. More recently, however, drugs known as aromatase inhibitors have produced superior results to tamoxifen alone in the treatment of ER-positive, postmenopausal breast cancer. Aromatase inhibitors interfere with the production of estrogen. Currently available aromatase inhibitors include Arimidex® (anastrozole), Aromasin® (exemestane), and Femara® (letrozole).
When considering how best to use aromatase inhibitors in the treatment of postmenopausal breast cancer, researchers have considered several possibilities: aromatase inhibitors could be used for extended hormonal therapy, after a woman has completed tamoxifen treatment; women could be switched to aromatase inhibitors after a brief (two- to three-year) period of tamoxifen therapy; or aromatase inhibitors could be used in place of tamoxifen as initial hormone therapy.
While it’s still uncertain which of these approaches is best, each of them appears to produce better outcomes than use of tamoxifen alone. The primary benefit observed thus far is a reduction in the risk of cancer recurrence. Researchers continue to evaluate which order and/or schedule will provide optimal outcomes for patients with breast cancer; their focus is on survival.
Researchers affiliated with the Intergroup Exemestane Study recently conducted a clinical trial to further evaluate switching to an aromatase agent after two to three years of treatment with tamoxifen. This trial included 4,724 postmenopausal women with hormone-positive breast cancer who had received tamoxifen for two to three years. One group of patients continued to receive tamoxifen for five years, while the other group switched to Aromasin for the remainder of the five-year treatment period. At a follow-up of approximately 56 months, the following results were reported:
- Patients who switched to Aromasin had a 15% reduced risk of death compared to those who continued to take tamoxifen.
- Cancer-free survival was improved by 24% among patients who switched to Aromasin compared to those who remained on tamoxifen.
The researchers concluded that these results provide further evidence that switching to an aromatase agent after two to three years of treatment with tamoxifen improves outcomes compared to continuing treatment with tamoxifen for five years. Specifically, results from this study demonstrated an improvement in survival. However, it is important that each patient who is currently being treated with hormone therapy or considering treatment with hormone therapy discuss her individual risks and benefits of every treatment option.
Reference: Coombes R, Kilburn L, Snowdon C, et al. Survival and safety of exemestane versus tamoxifen after 2-3 years’ tamoxifen treatment (Intergroup Exemestane Study): a randomised controlled trial. Lancet[early online publication]. February 13, 2007. DOI: DOI:10.1016/S0140-6736(07)60200-1.
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