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Ask The Pharmacist: New Tamoxifen Guidelines

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Michael White; Dept. Of Pharmacy Practice, UConn School Of Pharmacy


This past week there was major news from the American Society of Clinical Oncology for the 2.8 million women who have survived breast cancer and want to prevent its recurrenc

  1. What is Tamoxifen and how does it work?

Tamoxifen is a select estrogen receptor modulator, it blocks estrogen receptors in breast tissue but not in bone tissue. In effect, it gives breast cancer benefits without increasing the risk of osteoporosis.

  1. What is the new news regarding Tamoxifen?

70% of women with breast cancer have cancer cells that are estrogen receptor positive. That means that when estrogen stimulates those cancer cells it supercharges their growth. So after you have been diagnosed with breast cancer and receive chemotherapy, surgery, or radiation, patients with estrogen receptor positive cells who have a recurrence risk over 5-years of greater than 1.7% usually receive tamoxifen for 5 years. The results of major high quality clinical trials found that 5-years of therapy prevented recurrences versus placebo, or sugar pill. However, it was unclear whether continuing for a longer time period would yield additional benefits.   In two recent high quality trials they found that the benefits of 10-years of tamoxifen therapy versus the standard 5 years were greater than the risks. There was an overall survival advantage and a reduction in recurrence of breast cancer leading the major clinical cancer organization to recommend 10 years of therapy as a standard.

  1. Are there risks with Tamoxifen? What do you do if you need it but can’t take it?

Tamoxifen can cause some annoying but not serious symptoms like vaginal dryness and hot flashes. More concerning is that tamoxifen increases the risk of blood clots and uterine cancer. So while the average person with estrogen receptor positive breast cancer lives longer on tamoxifen therapy, 1 in 500 women will die from blood clots or uterine cancer. People with a history or high risk of blood clots, or people with uterine polyps should not take tamoxifen but may be candidates for other classes of effective drugs called aromatase inhibitors, pure estrogen blockers, or ovarian suppression drugs. You will need to discuss these options with your oncologist.


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