New Trials Highlight Breast Cancer Therapy and Prevention

Abstract

Antihormone Therapy for Breast Cancer Prevention Many women who face particularly high odds of developing breast cancer—including those having 2 or more blood relatives with breast cancer, a mother or sister who developed breast cancer before the age of 50 years, or a mother or sister who had breast cancer in bothbreasts—arewilling to take preventive measures. Some have prophylacticmastectomies. Someopt for longterm use of the antihormone therapies tamoxifen or raloxifene, which respectively lower breast cancer risk by 50% and 38% but can cause significant adverse effects such as blood clots and stroke. The phase 3 International Breast Cancer Intervention Study II (IBIS-II) Prevention trial investigatedwhether anastrozole, an alternative antihormone therapy with fewer adverseeffects than tamoxifenor raloxifene, helpspreventbreast cancer in such women. Anastrozole, an aromatase inhibitor that blocks estrogen production, has been used for more than a decade to preventbreast cancer recurrence inpostmenopausal womenwith tumors that are dependent on estrogen. From 2003 to 2012, researchers enrolled 3864 postmenopausal women at increased risk fordevelopingbreast cancer.Of these, 1920were randomlyassigned to take anastrozole for 5 years,while 1944were assigned to take a placebo. The results “were as good as we could havehopedfor,” saidJackCuzick,PhD,chairmanof the IBIS-IISteeringCommitteeanddirector of theWolfson Institute of Preventive Medicine at Queen Mary University of London.Theinvestigatorsfoundthatwomentaking anastrozole were 53% less likely to develop breast cancer than women taking placebo, with 40women in the anastrozole groupdevelopingbreastcancervs85women in theplacebogroup.Women in theanastrozolegroupwerealsosignificantly less likelyto develophigh-gradetumors.Theresultswere recentlypublishedtocoincidewiththeirpresentation at the conference (Cuzick J et al. Lancet.doi:10.1016/S0140-6736[13]62292-8 [published online December 12, 2013]). Mysteriously, the researchers found about a 40% reduction in other cancers as well, especially skin cancers. “This is anotherexcitingpossibility—that thismayhave an effect on other cancers, which we will continue to explore,” said Cuzick. The teamwill continue followingup the IBIS-II Preventionparticipants for at least 10 years to determine if anastrozole continues to influence cancer incidence even after treatment ends, if it reduces deaths from breast cancer, and if it is free from longterm adverse effects. Thestudy results comeshortly after the AmericanSocietyofClinicalOncologyadded exemestane,anotheraromatase inhibitor, to its list of recommended drugs to prevent breast cancer (http://bit.ly/1cRSNbX). That decision, announced in July, was based on the results of an earlier randomized study that showed a 53% reduction over a 3-year period in invasive and noninvasive breast cancer incidence with exemestane compared with placebo (Goss PE et al. N Engl J Med. 2011;364[25]:2381-2391).