Tamoxifen Switch Improves Breast Cancer Outcome

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Tamoxifen Switch Improves Breast Cancer Outcome

Reuters Health

By Karla Gale

Wednesday, March 10, 2004

NEW YORK (Reuters Health) - After women with breast cancer have been treated with tamoxifen for two years, switching to another anti-estrogen drug -- exemestane -- reduces the risk of the disease recurring or of new cancers arising, an international research team reports.

Lead author, Dr. R. Charles Coombes told reporters that clinicians should "consider switching treatment to exemestane between 2 and 3 years after the start of tamoxifen therapy for the 80 percent of postmenopausal women whose cancers contain estrogen receptors."

As the investigators explain in their article in this week's New England Journal of Medicine, many breast cancers are driven by the female hormone estrogen. Tamoxifen blocks the action of estrogen, but after several years some women have a relapse. An alternative group of drugs called aromatase inhibitors, which includes exemestane, prevents the production of estrogen.

The current study is the third major trial terminated early because of significantly better results achieved by using an aromatase inhibitor, either instead of or added to tamoxifen. The earlier trials evaluated letrozole and anastrozole, two reversible inhibitors, whereas exemestane is an irreversible inactivator.

Coombes, director of the Cancer Research UK Laboratories at Imperial College London, and his associates studied 4742 postmenopausal women who underwent complete surgical removal of a primary breast cancer and who were free of disease after tamoxifen treatment for 2 to 3 years. The participants were then randomly assigned to switch to exemestane or to continue on tamoxifen.

After an average follow-up of 30 months, disease had recurred in 266 women in the tamoxifen group but in only 183 women in the exemestane group -- a 32 percent reduction.

Exemestane also reduced the risk of cancer spreading beyond the breast, of cancer arising in the other breast, and of developing uterine and other cancers.

The decrease in the number of women with a second non-breast cancer was unexpected, Coombes said. He noted, however, that the small numbers and relatively short follow-up preclude any firm conclusions regarding this issue at this time.

In a Journal editorial, Dr. Martine J. Piccart-Gebhart, from the Jules Bordet Institute in Brussels, Belgium, proposes that "women whose risk of recurrence is high are reasonable candidates for the inclusion of an aromatase inhibitor" in their treatment.

However, when risk of recurrence is low, Piccart-Gebhart suggests that patients "may be better served by tamoxifen therapy," because of side effects with aromatase inhibitors.

But Coombes disagrees. "I would definitely recommend an aromatase inhibitor after two years of tamoxifen for patients undergoing adjuvant therapy after treatment of primary breast cancer," he told Reuters Health.

The anti-estrogen effects of aromatase inhibitors can have a negative impact on bone strength, but as long as women's bone mineral density is routinely assessed, "this is a class of drugs that ought to be used to prevent breast cancer."

"Metastatic breast cancer is completely devastating--a death sentence," he told reporters. "We agree it is early and that we don't know the long-term side effects, but you have to set it in the context of the devastating effect of metastatic breast cancer."

(Additional reporting by Richard Woodman)

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