COMMENTARY

Tamoxifen Prevents Breast Cancer: Worth a Chat With Patients

Lidia Schapira, MD

Disclosures

February 23, 2015

Tamoxifen for Prevention of Breast Cancer: Extended Long-term Follow-up of the IBIS-I Breast Cancer Prevention Trial

Cuzick J, Sestak I, Cawthorn S, et al
Lancet Oncol. 2015;16:67-75

Study Summary

IBIS-I was a randomized controlled trial that enrolled premenopausal and postmenopausal women 35-70 years of age between 1992 and 2001, who were considered to be at an increased risk of developing breast cancer, and randomly assigned them to receive tamoxifen or placebo for 5 years. The study enrolled over 7000 women. This publication reports the results after a median follow-up of 16 years.

There were 601 breast cancers reported, 251 (7.0% of the 3579 patients) in the tamoxifen group and 350 (9.8% of the 3575 patients) in the placebo group. The risk of developing breast cancer was similar in both groups between years 0-10 and after 10 years. The greatest reduction in risk was seen in invasive ER-positive breast cancer and noninvasive cancer (ductal carcinoma in situ), but no effect was noted for ER-negative breast cancer.

The results show that tamoxifen offers a very long period of protection after treatment cessation, lending further support to its use as an agent to reduce breast cancer risk in selected populations.

Viewpoint

Four previous randomized controlled trials[1,2,3,4] have shown that tamoxifen can reduce the risk ER-positive breast cancer in the first 10 years of follow-up. This important IBIS-I study confirms that the benefit is extended for more than 10 years, especially in reducing risk for invasive ER-positive cancers. The authors calculate that 22 women need to be treated for 5 years to prevent one breast cancer in the next 20 years. The profile of side effects and toxicities is identical to those reported previously.

Abstract

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