International Breast cancer intervention study (IBIS) II

30 March 2007



Evaluating whether the drug anastrozole can prevent breast cancer in women at elevated risk.

Scientific Title

ANZ02P2: An international multi-center study of anastrozole versus placebo in postmenopausal women at increased risk of breast cancer


Worldwide breast cancer is the commonest form of cancer in women with an estimated more than 1,400,000 cases and 370,000 deaths annually. Breast cancer is responsible for about 20% of the deaths from cancer in women in developed countries. Early detection and wider use of chemotherapy and hormone therapy have led to a reduction in breast cancer mortality. A further improvement might be gained from yet more effective use of adjuvant therapies. Early detection through the national breast cancer screening programme can also lead to similar reductions in mortality. However, neither of these approaches will affect cancer incidence. It is clear that with currently available treatments, the prospects for making a major impact on the breast cancer treatment side effects and mortality from breast cancer lie more in the area of prevention. The IBIS-II continues the work started in IBIS-I (Tamoxifen prevention trial) in determining whether a medical prevention option towards breast cancer is beneficial.

Recent publication

Cuzick J, Sestak I, Forbes JF, Dowsett M, Cawthorn S, Mansel RE, Loibl S, Bonanni B, Evans DG, Howell A, on behalf of the IBIS-II investigators. Use of anastrozole for breast cancer prevention (IBIS-II): long-term results of a randomised controlled trial. The Lancet. 2020; 395(10218):117-122,


IBIS II mammographic breast density sub-study

As part of the main IBIS II prevention protocol, breast density as a marker of increased risk for breast cancer was investigated.


Closed (for IBIS II prevention and sub-studies)