MONDAY, Oct. 24, 2005 (HealthDay News) -- Younger women with a certain type of early-stage breast cancer do better on five years of tamoxifen than those who stop treatment after two years, Italian researchers report.

Although it took nine years for the benefits to appear, investigators found that longer-term treatment makes a significant difference in the overall survival of women aged 55 and younger who have "estrogen receptor positive" tumors. Five years of treatment was associated with a 44 percent reduction in the risk of death among these women.

"Our study confirms that these women have to know that the longer use of tamoxifen is a great weapon to fight their battle," said study co-author Dr. Miriam Valentini, a staff scientist in the Laboratory of Clinical Epidemiology of Diabetes and Cancer at Consorzio Mario Negri Sud in Santa Maria Imbaro, Italy.

The study appears in the Dec. 1 edition of CANCER.

Breast cancers that need the female hormone estrogen to grow are known as estrogen receptor (ER) positive. The drug tamoxifen helps prevent the growth of estrogen-sensitive breast tumors.

When used as an additional therapy for treating early-stage breast cancer, tamoxifen is usually prescribed for five years, although the National Cancer Institute says the ideal length of treatment is not known.

To test whether duration makes a difference in treating early-stage breast cancer, researchers randomly assigned 1,901 patients to stop tamoxifen after two years or receive an additional three years of drug therapy.

The benefits of longer therapy on overall survival of ER-positive patients only started to emerge after nine years from diagnosis of the disease. And within that group, only younger women benefited.

V. Craig Jordan, scientific director for medical science at Fox Chase Cancer Center in Philadelphia, said the difference between younger and older women is in their endocrinology.

"In pre-menopausal women, they are awash in estrogen," he explained, and that hormone's relationship to breast cancer is like that of lighter fluid to fire. "You need five years (of tamoxifen) to act really as the fire blanket to keep all this estrogen away," he added, noting that older women, by contrast, need less.

That's not to say older women should stop treatment after two years. Physicians should carefully weigh the risks and benefits for women over 55, including the known side effects of endometrial cancer and blood clots, Valentini said.

"After a careful evaluation of these aspects, they can decide if, for an individual patient, it is suitable to prolong therapy with this drug or to use another hormonal drug," she added.

The authors concluded that more research is needed to explore the effects of hormonal therapy in breast cancer.

"This as a single piece of evidence shouldn't change the standard of care in America," Jordan added.

More information

For more on tamoxifen treatment, visit the National Cancer Institute.

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