Exemestane
Following Tamoxifen Improves Cancer-Free Survival in Breast
Cancer
According to a recent article published in The New England
Journal of Medicine, exemestane (Aromasin ®) following
2 to 3 years of tamoxifen (Nolvadex ®) improves cancer-free
survival compared to continued tamoxifen in estrogen receptor-positive
breast cancer.1
Breast cancer claims the lives of approximately 40,000 women
annually in the United States alone. One common type of breast
cancer, referred to as estrogen receptor-positive (ER-positive),
is stimulated to grow from the naturally occurring female
hormone estrogen. One component of treatment for women with
ER-positive breast cancer is hormone therapy, in which levels
of estrogen are either reduced in the body, or estrogen is
prevented from binding to a cancer cell, thus inhibiting growth-stimulatory
effects. At present, the anti-estrogen tamoxifen is the standard
hormone agent for treatment of women with ER-positive early
breast cancer. However, a newer class of agents, called aromatase
agents, has emerged into the clinical setting for treatment
of HR-positive breast cancer. Aromatase agents work by inhibiting
the enzyme (protein) aromatase, which is involved in the production
of estrogen in the body. Aromatase agents are approved for
treatment of different stages of breast cancer and clinical
trials are ongoing to determine the optimal length and sequencing
of tamoxifen and aromatase agents for treatment of ER-positive
breast cancer.
Previous clinical trials have demonstrated that treatment
with tamoxifen for over 5 years does not improve outcomes
compared to treatment with tamoxifen for up to 5 years. Furthermore,
a recent clinical trial demonstrated that women with ER-positive
breast cancer who switched to the aromatase agent anastrozole
(Arimidex ®) following treatment for at least 2 years with
tamoxifen had improved outcomes compared to those who continued
on tamoxifen for the duration of 5 years. 2
More recently, researchers affiliated with the Intergroup
Exemestane Study conducted a clinical trial to evaluate the
aromatase agent exemestane in women with ER-positive breast
cancer who had been treated with 2 years of tamoxifen. Exemestane
is currently FDA approved for the treatment of advanced breast
cancer in postmenopausal women that has continued to grow
following treatment with tamoxifen. This trial included over
4,742 women who had early-stage breast cancer, meaning their
cancer had not spread to distant or several sites in the body.
They had all received 2 to 3 years of treatment with tamoxifen;
approximately half switched to exemestane for the duration
of 5 years, and approximately half continued to receive tamoxifen
for a total of 5 years. Following approximately 3 years of
follow-up, cancer-free survival was improved by 32% in the
patients who switched to exemestane, compared to those who
continued on tamoxifen. Breast cancer in the opposite breast
occurred in 9 patients who switched to exemestane, compared
to 20 patients who continued on tamoxifen. Exemestane was
very well tolerated.
The researchers concluded that switching to exemestane following
2 or 3 years of treatment with tamoxifen in early ER-positive
breast cancer results in improved cancer-free survival. Patients
with ER-positive breast cancer should discuss the risks and
benefits of treatment including exemestane or other aromatase
agents with their physician.
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