Anastrozole for prevention of breast cancer in high-risk postmenopausal women (IBIS-II): an international, double-blind, randomised placebo-controlled trial
- Study type
- Clinical trial
- Study name
- IBIS-II
- Design
- International, double-blind, randomised (1:1), placebo-controlled trial; intention-to-treat analysis; registration number ISRCTN31488319
- Sample size
- 3864 women (1920 in the anastrozole group and 1944 in the placebo group)
- Source
- The Lancet · 2014
In plain words
In this study, postmenopausal women at high risk of breast cancer took an anastrozole tablet or a placebo (a tablet with no active drug) every day for 5 years. In the anastrozole group, about half as many women developed breast cancer as in the placebo group (40 versus 85 women). The number of deaths was about the same in the two groups, and most side effects due to lower oestrogen were not attributed to the drug. The decision to take this drug should be made with your doctor, based on each person's level of risk.
Key results
Treatment arms and regimens
Oral anastrozole 1 mg daily for 5 years (1920 women).
Matching oral placebo daily for 5 years (1944 women).
Source of the regimen details: Abstract of the paper
Doses are given for the information of specialists, as in this study’s protocol, and are not a prescription. Every drug must be prescribed by the treating physician for the individual patient.
Study population
Postmenopausal women aged 40 to 70 years from 18 countries who were at increased risk of breast cancer according to defined criteria. Recruitment took place from 2 February 2003 to 31 January 2012.
Endpoints
Primary endpoint: histologically confirmed breast cancer (invasive cancers or non-invasive ductal carcinoma in situ (DCIS)). Randomisation was stratified by country and done in blocks of six, eight or ten. Only the trial statistician was aware of treatment allocation.
Safety and side effects
The abstract does not report exact numbers of grade 3 or higher adverse events. Based on the abstract, most adverse events related to oestrogen deprivation were not attributed to treatment. The number of deaths was similar in the two groups (18 versus 17). Details of adverse events are available in the full text of the paper.
Clinical significance and place in guidelines
Based on the abstract, anastrozole effectively reduced the incidence of breast cancer in high-risk postmenopausal women, and the authors consider this finding to support its use in this group. The exact status of this use in clinical guidelines and drug licences should be checked in up-to-date sources; the abstract gives no information on them.
Limitations
The abstract does not report exact numbers of adverse events, and a full safety assessment requires the full text of the paper. Median follow-up was 5.0 years. This paper has corrections (Erratum) (Lancet 2014;383:1040 and Lancet 2017;389:1010), which should be checked in the full text when citing it.
This summary was prepared by the editorial team from the published paper; the original paper is the final reference. Read the original abstract on PubMed.