A panel of experts told the Food and Drug Administration Wednesday that the label of cancer drug Tamoxifen should be changed to include evidence that certain women with estrogen-related breast cancer may be at higher risk for recurrence of the disease.
Tamoxifen is designed to block estrogen in women with the most common type of breast cancer. By blocking estrogen, the drug controls tumor growth. The drug, usually taken for five years, is used as additional therapy following primary treatment for breast cancer. It is also used for the reduction in breast cancer incidence in high-risk women.
Studies, however, have suggested that the drug isn’t as effective in patients who have poor activity of an enzyme called CYP2D6. That enzyme is responsible for metabolizing tamoxifen into endoxifen, which suppresses estrogen-dependent cell proliferation.
In general, some women are CYP2D6-poor metabolizers because of genetic predisposition.
The advisory panel was first asked whether the tamoxifen label should include information about increased risk for breast cancer recurrence in CYP2D6-poor metabolizers. They were then asked whether there is sufficient scientific and clinical evidence to support revisions of the tamoxifen label recommending that women be tested for the enzyme capabilities before being prescribed the drug.
While many of the panel members said more trials should be conducted on the issue, they overall agreed that the label should be modified.
“The risk signal needs to be indicated very clearly to patients,” said panel member Howard McLeod, a director at University of North Carolina’s Institute for Pharmacogenomics & Individualized Therapy. “Patients may choose to continue with tamoxifen for other reasons, but at least they need to be informed of the risk that is present.”
On the testing recommendation, McLeod said “I believe this information should suggest testing, but not require testing. The data is not there to make it malpractice not to test, but the data is there to suggest that it should be taken into strong consideration.”
McLeod said the testing would cost as much or even less than other testing breast cancer patients undertake. “It is a very little added expense, and yet it can help making a more objective decision on the therapy.”
The panel’s decision isn’t official and doesn’t indicate the FDA will seek a change on the drug’s label.
The agency first approved tamoxifen under the brand name Nolvadex in 1977 by then-manufacturer Zeneca Pharmaceuticals, which later merged with Astra to form U.K.-based AstraZeneca PLC (AZN).
Since then, other companies, including a unit of Barr Laboratories Inc. (BRL) and Teva Pharmaceutical Industries Ltd. (TEVA), have been allowed to sell tamoxifen as a generic drug. AstraZeneca stopped selling the drug in June because of declining sales.
Matthew Goetz, assistant professor of oncology at Mayo Clinic College of Medicine, said it is important to discuss the efficacy of tamoxifen in women who have poor enzyme activity because there are now other treatments available that could be more effective for those patients.
“Tamoxifen is not the only kid on the block anymore,” he said in a presentation.
According to Goetz, while pre-menopausal women who have estrogen-positive breast cancer still have Tamoxifen as their only treatment option, post-menopausal women can also take newer drugs known as aromatase inhibitors.
Last year, the FDA approved the drugs, which include AstraZeneca’s Arimidex, Novartis AG’s (NVS) Femara and Pfizer Inc.’s (PFE) Aromasin, to treat post-menopausal women with early-stage breast cancer. The drugs were originally approved to treat more advanced cases of breast cancer and in some cases to use after women had been on tamoxifen for five years.