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Tamoxifen Increases Tumor Growth in Some Breast Cancer Patients

Dec 4, 2008 | Parker Waichman LLP Tamoxifen, a drug routinely given to breast cancer patients, could actually increase tumor growth in certain patients, a new study has found.  The authors of the study, which was published in the journal Breast Cancer Research, said their work could eventually lead to tests that could screen out patients who might be endangered by taking tamoxifen.

According to the National Cancer Institute website, Tamoxifen has been used for more than 30 years to treat breast cancer in women and men.  Tamoxifen interferes with the activity of estrogen, a female hormone. Estrogen can promote the development of cancer in the breast. Tamoxifen is approved by the U.S. Food and Drug Administration (FDA) for the prevention of breast cancer and for the treatment of breast cancer, as well as other types of cancer.

According to, tamoxifen is given to most patients for five years after they are diagnosed with breast cancer to prevent the disease from returning.  However, some develop resistance, which means their tumor is more likely to recur. Last month, a British team identified a called Pax2  which contributed to the development of such resistance, Reuters said.

According to this latest tamoxifen study, use of drugs like tamoxifen in patients with low levels of another protein - E-cadherin - may promote more harmful cancer cell behavior. The E-cadherin protein makes cells stick together. In their experiments, researchers from Cardiff University found  that when the protein was at reduced levels, tamoxifen caused cancer cells to move around much more aggressively.  This activity can lead to tumor growth, they said.

The researchers said that the next stage of their work would be to determine an actual level of the protein that would cause tamoxifen to fail.  Further research could lead to the development of screening tests to identify breast cancer patients who should be given alternatives to drugs like tamoxifen.

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