Research has shown that five years is the optimal amount of time t Study: Many Breast Cancer Patients Quit Treatment with Tamoxifen (dateline March 31, 2007) | Breast Health News | Imaginis - The Women's Health & Wellness Resource Network

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Study: Many Breast Cancer Patients Quit Treatment with Tamoxifen (dateline March 31, 2007)

Research has shown that five years is the optimal amount of time to take tamoxifen to help treat breast cancer and prevent its recurrence, but a new study from Ireland finds that many women stop taking tamoxifen early. The study showed that after one year of treatment, over 22% of women in an Irish study had discontinued tamoxifen. After 3.5 years, over one-third had stopped taking the drug. Past studies have shown that many women stop taking tamoxifen due to side effects. However, the researchers caution that tamoxifen is most effective when taken for five years. They believe that effective strategies are needed to reduce side effects and noncompliance. They also suggest that their study results have implications for patient compliance with other oral medications.

Tamoxifen is a drug taken orally in pill form. For over a quarter century, physicians have prescribed tamoxifen to help treat patients with advanced breast cancer. In the 1990s, physicians began using tamoxifen to treat early stage breast cancer after breast surgery (lumpectomy or mastectomy). Tamoxifen has been shown to help prevent the original breast cancer from returning after breast surgery while also hindering the development of new cancers in the opposite breast. In late 1998, tamoxifen became the first drug to be approved by the U.S. Food and Drug Administration (FDA) to prevent breast cancer after research showed it reduced the chances of developing breast cancer by 50% in women at high risk.

Though the overall occurrence of side effects with tamoxifen is relatively low, as with all drugs, there are potential negative effects associated with tamoxifen. The most common side effect of tamoxifen is a higher occurrence of hot flashes. Other side effects include irregular menstrual cycles, unusual vaginal discharge or bleeding, and irritation of skin around the vagina.

In addition, tamoxifen also slightly increases a woman's chances of developing serious health problems. The following table shows potential serious health problems associated with tamoxifen and the likelihood of occurrence, based on data from the National Surgical Adjuvant Breast and Bowel Project.


Incidence in women taking tamoxifen

Incidence in women not taking tamoxifen

Endometrial cancer

2.29/1000 cases annually

0.92/1000 cases annually

Pulmonary embolism

0.75/1000 cases annually

0.25/1000 cases annually

Deep-vein thrombosis

1.26/1000 cases annually

0.79/1000 cases annually


1.43/1000 cases annually

1.00/1000 cases annually


25.41/1000 cases annually

22.51/1000 cases annually

Cataract surgery

46.62/1000 cases annually

31.43/1000 cases annually

*source: Fisher B, Costantino JP, Wickerham DL, et al. Tamoxifen for prevention of breast cancer: report of the National Surgical Adjuvant Breast and Bowel Project P-1 study. J Natl Cancer Inst. 1998;90:1371-1388. Nolvadex prescribing information, AstraZeneca Pharmaceuticals LP, Wilmington, Delaware.

While studies vary, five years of tamoxifen use has been shown to reduce the risk of a breast cancer recurrence by 46% and the relative risk of death of 26%. Given tamoxifen's side effects and past studies that have shown women's reluctance to take tamoxifen for five full years, Thomas I. Barron of St. James Hospital in Dublin, Ireland, and his colleagues conducted a large study on tamoxifen compliance. They focused on 2,816 women 35 years of age or older who began taking tamoxifen for breast cancer between January 2001 and January 2004. The researchers studied the rate of prescription refills among the women to determine whether they continued to take tamoxifen or not.

The results of the study found that 22% of women discontinued tamoxifen after the first year of treatment, and 35% discontinued tamoxifen after three and a half years of treatment. Younger women (ages 35-44) were more likely to discontinue tamoxifen than older women, as were women who were taking antidepressants within a year before beginning tamoxifen.

The researchers say that given the results of the study and the benefits of continuing tamoxifen treatment, effective strategies for reducing tamoxifen's side effects are needed to increase tamoxifen continuance. They also noted that physicians should be aware of the potential for patients to stop taking other oral hormonal medications.

Women who are considering tamoxifen should discuss all potential benefits and risks with their physicians prior to treatment. In many cases, the benefit of treating or preventing breast cancer with tamoxifen outweighs the risk of these side effects.

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