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Breast Cancer 101 (Interactive Multimedia) - Tamoxifen
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Tamoxifen (Nolvadex) has been used for over 30 years to treat breast cancers that are hormone-receptor positive. Figure 5.9 below shows how tamoxifen works. It attaches to the hormone receptor in the cancer cell, blocking estrogen from attaching to the receptor. Since hormone-receptor positive cells need estrogen to grow, tamoxifen can slow or stop the growth of cancer cells.  

Unlike aromatase inhibitors, tamoxifen can be used to treat breast cancer in both premenopausal and postmenopausal women.  

Tamoxifen is also used to treat breast cancer in men. Learn more about breast cancer in men

Figure 5.9 

Illustration of tamoxifen 

Source: British Broadcasting Corporation

Tamoxifen as breast cancer treatment

Treatment with tamoxifen lowers the risk of [60]:

Tamoxifen is a pill taken every day for up to five years. The benefits from tamoxifen last long after you stop taking it.  

Clinical trials continue to explore the use of tamoxifen beyond five years. Recent findings from a large randomized clinical trial showed that taking tamoxifen for an additional five years (for a total of 10 years) further reduced the risk of breast cancer recurrence and death [64]. However, there was a continued risk of health effects, such as endometrial cancer [64]. Women should discuss the benefits and risks of taking tamoxifen for more than five years with their health care providers.

Tamoxifen and antidepressant use

Some types of antidepressants called selective serotonin reuptake inhibitors (SSRIs) can interfere with the metabolism of tamoxifen (how tamoxifen works in the body). Some SSRIs (such as Prozac, Paxil and Zoloft) interfere with tamoxifen to such a degree that they should not be taken while on tamoxifen [44,65]. If you are taking an SSRI to treat depression or menopausal symptoms, talk to your health care provider about possible drug interactions and other treatment options.  

Learn about SSRI antidepressants for the treatment of menopausal symptoms.

Tamoxifen as a risk-lowering drug

Among cancer-free women who have a high risk of developing breast cancer (including those with atypical hyperplasia or lobular carcinoma in situ) tamoxifen can be taken to lower risk [66-67].  

Learn more about risk-lowering drugs and other options for women at high risk of breast cancer.

Learn more about tamoxifen on the National Institutes of Health's Medline Plus website   

Side effects of tamoxifen

The side effects of tamoxifen differ from those of other hormone therapies. Learn more about the side effects of tamoxifen   

Importance of following your breast cancer treatment plan

The importance of adherence (compliance)

Breast cancer treatment is most effective when all parts of the treatment plan are followed. Adherence (also called compliance) is how closely people follow the treatment plan (for medications and other therapies) prescribed by their health care providers in terms of:

  • Timing
  • Dose
  • Frequency

Completing tamoxifen treatment

Tamoxifen is typically prescribed for up to five years for breast cancer treatment. The length of treatment coupled with side effects can make adherence to tamoxifen difficult. Although the menopausal symptoms related to tamoxifen can be hard to deal with, there are treatments that may ease these side effects. If you have side effects, talk to your health care provider about ways to treat them.

To get the most benefit out of your treatment, you need to take the full course of hormone therapy. Women who complete the full course have higher rates of survival [63].  

If you have trouble remembering to take your tamoxifen, a daily pillbox or setting an alarm on your watch or phone may help [3]. However, you do not need to panic if you miss a day or two. 

Learn more about adherence.


For more information on tamoxifen, visit the National Comprehensive Cancer Network (NCCN) or the American Society for Clinical Oncology (ASCO).

Updated 03/28/14


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