Tamoxifen: new warning label for chemoprevention drug


by Dalene Entenmann, The Cancer Blog, 21 Oct 2006

MarketWatch is reporting that a panel of experts has recommended that the drug labeling for Tamoxifen be changed to include warnings some women with estrogen-positive breast cancer might be at greater risk for breast cancer recurrence. The recommendation comes as a result of studies that show the drug is not as effective for women with estrogen-positive breast cancer if they also carry an enzyme, called CYP2D6, that does not actively metabolize tamoxifen as it should to make the drug work in preventing breast cancer.

ccording to the report, the panel's decision isn't official and doesn't indicate the Food and Drug Administration (FDA) will seek a change on the drug's label.

However, one of the panel members suggested that while testing women to see if they are at greater risk, due to poor activity of CYP2D6, should not be mandatory, women need to be made aware of the risks and that testing of this enzyme is available.

This might be an especially important consideration for pre-menopausal women, as Tamoxifen is the only estrogen-blocking drug available to them right now for the prevention of estrogen-positive breast cancer recurrence.