Aromatase inhibitors effectively prevent breast cancer recurrence and development of new contralateral tumours in postmenopausal women.
Researchers have assessed the efficacy and safety of the aromatase inhibitor Anastrozole ( Arimidex ) for prevention of breast cancer in postmenopausal women who are at high risk of the disease.
During the period 2003-2012, postmenopausal women aged 40-70 years from 18 countries into an international, double-blind, randomised placebo-controlled trial ( IBIS-II ): were recruited. To be eligible, women had to be at increased risk of breast cancer ( judged on the basis of specific criteria ).
Eligible women were randomly assigned ( 1:1 ) by central computer allocation to receive 1 mg oral Anastrozole or matching placebo every day for 5 years.
Randomisation was stratified by country and was done with blocks ( size six, eight, or ten ).
All trial personnel, participants, and clinicians were masked to treatment allocation; only the trial statistician was unmasked.
The primary endpoint was histologically confirmed breast cancer ( invasive cancers or non-invasive ductal carcinoma in situ ).
Analyses were done by intention to treat.
1920 women were randomly assigned to receive Anastrozole and 1944 to placebo. After a median follow-up of 5.0 years, 40 women in the Anastrozole group ( 2% ) and 85 in the placebo group ( 4% ) had developed breast cancer ( hazard ratio, HR=0.47; p less than 0.0001 ).
The predicted cumulative incidence of all breast cancers after 7 years was 5.6% in the placebo group and 2.8% in the Anastrozole group.
18 deaths were reported in the Anastrozole group and 17 in the placebo group, and no specific causes were more common in one group than the other ( p=0.836 ).
In conclusion, Anastrozole effectively reduces incidence of breast cancer in high-risk postmenopausal women.
This finding, along with the fact that most of the side-effects associated with oestrogen deprivation were not attributable to treatment, provides support for the use of Anastrozole in postmenopausal women at high risk of breast cancer. ( Xagena )
Cuzick J et al, The Lancet 2014; 383: 1041-1048