Benefits Outweigh Risk With 10 Years of Tamoxifen, ACOG Says

Lara C. Pullen, PhD

May 29, 2014

Tamoxifen use can be extended safely to 10 years for some women with breast cancer, according to a new committee opinion from the American College of Obstetricians and Gynecologists (ACOG), published in the June issue of Obstetrics & Gynecology.

The updated committee opinion on tamoxifen and uterine cancer replaces one published in June 2006. It reflects newer data demonstrating additional benefit of tamoxifen use for an additional 5 years in women with breast cancer. ACOG reviews all committee opinions regularly, and there were no dramatic changes to the updated opinion, according to coauthor Jed Delmore, MD, from the University of Kansas School of Medicine in Wichita.

"[W]e wanted to clarify/reinforce that there was no need for additional, routine screening for women receiving tamoxifen in the absence of symptoms. There is some evidence to suggest an increased risk of developing a uterine neoplasm in women with existing endometrial polyps prior to the initiation of therapy with tamoxifen, which we wanted to note in the update," he told Medscape Medical News.

The committee notes that if a woman taking tamoxifen develops atypical endometrial hyperplasia, the clinician should manage that condition and reassess the use of tamoxifen.

Small Risk, Big Gain

Tamoxifen, a selective estrogen receptor modulator, is widely prescribed to women with breast cancer. Although it is primarily antiestrogenic, it also has mild estrogenic activity. As a consequence, it appears to result in a 2- to 3-fold increased relative risk of developing endometrial cancer.

The National Surgical Adjuvant Breast and Bowel Project trial B-14 showed a 1.6 per 1000 patient-years rate of endometrial cancer among tamoxifen users (20 mg/day) vs a 0.2 per 1000 patient-years rate among women taking a placebo at the 5-year point in the study.

At 10 years, the rate of an endometrial cancer rate in women treated with tamoxifen was 1.26 per 1000 patient-years, compared with 0.58 per 1000 patient-years in women who received placebo.

"In this study, the 5-year disease-free survival rate from breast cancer was 38% higher in the tamoxifen group than in the placebo group, suggesting that the small risk of developing endometrial cancer is outweighed by the significant survival benefit provided by tamoxifen therapy for women with breast cancer," the committee writes. "Continuation of tamoxifen therapy for 10 years further reduced the risk of breast cancer recurrence and mortality."

Although several approaches have been developed to screen for endometrial proliferation or endometrial cancer in asymptomatic women prescribed tamoxifen, none have proven effective, according to the committee. However, prescreening women before they initiate tamoxifen therapy may identify patients with benign polyps who are at higher risk for atypical hyperplasia.

On the basis of all these data, the committee recommends the following:

  • Tamoxifen use may be extended to 10 years on the basis of new data demonstrating additional benefits.

  • Clinicians should inform women taking tamoxifen about the risks for endometrial proliferation, endometrial hyperplasia, endometrial cancer, and uterine sarcomas.

  • Clinicians should investigate any abnormal vaginal bleeding, bloody vaginal discharge, staining, or spotting.

  • Clinicians should closely monitor postmenopausal women taking tamoxifen for symptoms of endometrial hyperplasia or cancer.

  • No additional monitoring is needed for premenopausal women taking tamoxifen, as there is no evidence to show they are at increased risk for uterine cancer.

The authors have disclosed no relevant financial relationships.

Obstet Gynecol. 2014;123:13941397. Full text

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