What is the role of tamoxifen in the adjuvant therapy for breast cancer?

Updated: May 21, 2019
  • Author: Erin V Newton, MD; Chief Editor: Neetu Radhakrishnan, MD  more...
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Tamoxifen is a selective estrogen receptor modulator (SERM) that binds to and inhibits estrogen receptor signaling in the breast. As a receptor antagonist, it is effective in both premenopausal and postmenopausal women. Tamoxifen has ER-stimulating effects in other tissues, which has both beneficial and adverse consequences: in bone, the stimulation results in preservation of bone density; in endometrium, it leads to a 2- to 4-fold increased risk of endometrial cancer.

A pilot study by Nielsen et al found that ESR1 amplification is associated with a poorer outcome following adjuvant treatment with tamoxifen among patients with ER-positive early breast cancer. [37] However, the prognostic and predictive impact of ESR1 copy number changes requires further study, and such testing is not considered standard of care.

Tamoxifen has been approved for breast cancer treatment since the early 1980s and has been shown in multiple studies to decrease breast cancer–associated mortality and recurrence. In an analysis of 55 trials evaluating tamoxifen versus placebo in the adjuvant treatment of breast cancer, 5 years of tamoxifen therapy resulted in a 47% reduction in recurrence and a 22% reduction in mortality.

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