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Tamoxifen is the most common drug treatment for advanced breast cancer. However, at some point, patients may
become resistant to tamoxifen and require additional drug options. A new study finds that
the drugs Femara (generic name, letozole) and Arimidex (generic name, anastrozole) both slow the
progression of advanced breast cancer that has been previously treated with tamoxifen. The
research shows confirms that Femara is more powerful than Arimidex in shrinking and
eliminating breast cancer tumors.
Femara was approved by the U.S. Food and Drug Administration (FDA) in 1997 to help
treat advanced breast cancer in women whose breast cancer tumors have not responded well
to tamoxifen. Femara works by reducing the total amount of estrogen in the body
(circulating estrogen levels), thereby limiting the amount of estrogen that can affect
breast cancer cells. In post-menopausal women, the body produces estrogen from other
hormones known as androgens by the action of an enzyme called aromatase. Femara is an
aromatase inhibitor and blocks aromatase from converting androgen into estrogen, thus
lowering the amount of estrogen in the body. Arimidex was also approved by the FDA to
treat advanced breast cancer after a first-line treatment with tamoxifen. Like Femara,
Arimidex is also an aromatase inhibitor and decreases the production of estrogen.
Researchers have known that Femara is a more powerful drug than Arimidex in terms of
shrinking breast cancer tumors. However, Dr. C. Rose, from the Lund University Hospital in
Sweden and colleagues wanted to determine whether both drugs could effectively slow the
progression of breast cancer in patients with advanced stages of the disease.
To conduct their study, Dr. Rose and colleagues studied 713 advanced breast cancer
patients who had been treated with tamoxifen as a first-line therapy. Then, the women were
treated with either Femara or Arimidex. Approximately 19% of the women who were treated
with Femara experienced a shrinkage or disappearance of their tumors while 12% of the
women treated with Arimidex experienced similar results. Cancer treated with either drug
took about six months to progress.
Thus, the researchers conclude that advanced breast cancer responds more effectively to
Femara than Arimidex as a second-line treatment, after using tamoxifen. Both drugs were
well-tolerated in the study and did not differ in terms of safety. In addition, the rate
of cancer progression was equal with both drugs.
Possible side effects of Femara may include:
- Musculoskeletal pain (pain in the skeleton or legs, arms or back)
- Nausea
- Headache
- Joint pain
- Fatigue
- Difficulty breathing
Possible side effects of Arimidex may include:
- General feeling of weakness
- Decreased energy level
- Headache
- Nausea
- Mild diarrhea
- Increased or decreased appetite
- Sweating
- Hot flashes
- Vaginal dryness
- Temporary hair thinning
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