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# Study Reveals Limitations of Tamoxifen
- URL: https://www.foodconsumer.org/270820090913_study_reveals_limitations_of_tamoxifen/
- Published: 2009-08-27T21:11:00.000Z
- Updated: 2026-09-22T16:00:06.000Z
- Description: In a Cancer Research study of 1,100 women with estrogen-sensitive tumors, five years of tamoxifen cut recurrence risk by 60 percent. Those same long-term users were four times more likely to develop a rare, aggressive breast cancer that is not estrogen sensitive, which tamoxifen cannot treat.
- Author: Food Consumer
- Tags: Drug, Health News, #vivvo-import

Rachel Stockton ([rachels@foodconsumer.org](mailto:rachels@foodconsumer.org))

Tamoxifen is the most prescribed and oldest selective estrogen receptor modulator (SERM) prescribed for women with breast cancer. The medication that blocks estrogen receptors in the breast and inhibits their growth, has come under some scrutiny of late. However, it's not so much the drug that has surprised researchers, it's breast cancer itself, which can vary surprisingly and diametrically, causing the drug to be ineffective at best, and in rare cases, a risk factor.

The journal Cancer Research is reporting on a study of 1100 women who had estrogen sensitive tumors. The risk of recurrence of estrogen sensitive breast cancer was 60% less for women who took Tamoxifen for 5 years.

However, those same long time users are 4 times MORE likely to develop a rare and very aggressive breast cancer that is not estrogen sensitive, thus rendering Tamoxifen ineffective.

Specifically, Tamoxifen is hormone therapy that is given to women right after breast cancer surgery and in some cases after chemo and radiation.

According to breastcancer.org, Tamoxifen can:

· reduce the risk of \[estrogen sensitive\] breast cancer coming back by 40% to 50% in post-menopausal women and by 30% to 50% in pre-menopausal women

· reduce the risk of a new cancer developing in the other breast by about 50%

· shrink large, hormone-receptor-positive breast cancers before surgery

· slow or stop the growth or advanced (metastatic) hormone-receptor-positive breast cancer in both pre- and post-menopausal women

· lower breast cancer risk in women who have a higher-than-average risk of disease but have not been diagnosed

For more information on estrogen sensitive breast cancer and Tamoxifen, visit [breastcancer.or](http://www.breastcancer.org/?ref=foodconsumer.org)g.