Tamoxifen’s Cancer-Fighting Effect Lessened by Two Proteins

High levels of two proteins known to affect the growth of breast cancer cells also inhibit the cancer-fighting potential of tamoxifen, a drug used to prevent recurrence and new breast cancers in women at risk, said researchers from Baylor College of Medicine in the March 5 issue of the Journal of the National Cancer Institute.

C. Kent Osborne, M.D., director of the Breast Center at Baylor College of Medicine, and his collaborators found that when a protein called AIB1 (Amplified in Breast Cancer-1) as well as another called HER-2 is present in high levels in the cells of women who have had breast cancer, their tumors are resistant to the cancer-fighting effects of tamoxifen.

“In fact, tamoxifen might have an adverse effect,” said Osborne. The finding could be important in predicting which women will respond to tamoxifen therapy. Before the finding can be used in patient treatment, it must be confirmed in studies with more patients, he said.

Osborne and his colleagues determined the AIB1 and HER-2 levels in the tumors of 316 breast cancer patients. They then correlated these levels with how long the women lived without recurrence of their disease. They found that women with high levels of AIB1 and HER-2 had worse outcomes with tamoxifen therapy than all other women combined. When the level of either protein is low, then the tamoxifen problem does not occur, Osborne said.

His co-authors include Drs. Valerie Bardou, Torsten A. Hopp, Gary C. Chamness, Susan G. Hilsenbeck, Suzanne A.W. Fuqua, Jiemin Wong, D. Craig Allred, Gary M. Clark and Rachel Schiff, all of Baylor.

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©2006 Texas Medical Center

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