{"entity":{"id":"ibis-ii","kind":"trial","name":"IBIS-II (International Breast Intervention Study II)","aka":["IBIS-2","IBIS-II Prevention","ISRCTN31488319"],"tldr":"The trial that made anastrozole a prevention drug, halving breast cancer in postmenopausal women at high risk and, with a licence granted in 2023, putting a generic tablet on the NHS prevention pathway.","summary":"IBIS-II randomised 3,864 postmenopausal women at increased risk of breast cancer to anastrozole or placebo for five years. After a median 131 months, 85 women in the anastrozole arm and 165 in the placebo arm had developed breast cancer, a hazard ratio of 0.51, with the benefit continuing after treatment stopped and no excess of fractures or cardiovascular disease in the post-treatment period. NICE CG164 recommendation 1.7.22, amended in 2023, tells the NHS to offer anastrozole for five years to postmenopausal women at high risk unless they have severe osteoporosis; the MHRA licensed anastrozole for prevention in 2023 through its repurposing programme.","status":"positive","asOf":"2026-09-25","links":[{"label":"Lancet 2020 (DOI)","url":"https://doi.org/10.1016/S0140-6736(19)32955-1"},{"label":"ISRCTN31488319","url":"https://www.isrctn.com/ISRCTN31488319"},{"label":"NICE CG164 recommendations","url":"https://www.nice.org.uk/guidance/cg164/chapter/Recommendations"}],"tags":["uk","breast","prevention"],"related":[],"cancers":["breast-cancer"],"sections":[],"technologies":[],"targets":[],"drugs":["anastrozole","tamoxifen"],"companies":[],"institutions":[],"pathways":[],"terms":[],"trials":[],"people":["jack-cuzick"],"bottlenecks":[],"keyPapers":[],"journals":[],"dependsOn":[],"notes":[],"nct":"ISRCTN31488319","phase":"3","setting":"Prevention: anastrozole 1 mg daily for five years against placebo in postmenopausal women at increased risk of breast cancer","sponsor":"Queen Mary University of London (Cancer Research UK funded)","result":"Breast cancer in 85 of 1,920 on anastrozole against 165 of 1,944 on placebo after a median 131 months, hazard ratio 0.51 (Lancet 2020).","yearReported":2020,"enrolled":3864,"enrolledBasis":"registry","outcomes":[]},"route":"/trials/ibis-ii/","neighbours":{"cancer":[{"id":"breast-cancer","kind":"cancer","name":"Breast cancer (all types)","route":"/cancers/breast-cancer/"}],"drug":[{"id":"anastrozole","kind":"drug","name":"Anastrozole","route":"/drugs/anastrozole/"},{"id":"tamoxifen","kind":"drug","name":"Tamoxifen","route":"/drugs/tamoxifen/"}],"person":[{"id":"jack-cuzick","kind":"person","name":"Jack Cuzick","route":"/people/jack-cuzick/"}]}}