{"registry": "ISRCTN", "registryId": "ISRCTN91879928", "source": "https://www.isrctn.com/ISRCTN91879928", "apiSource": "https://www.isrctn.com/api/trial/ISRCTN91879928/format/default", "fetchedAt": "2026-10-07T17:01:00.384125Z", "license": "CC BY 4.0", "licenseSource": "https://www.isrctn.com/page/faqs#licence-to-post", "study": {"title": "An international multicentre study of tamoxifen versus placebo in women at increased risk of breast cancer", "scientificTitle": "An international multicentre study of tamoxifen versus placebo in women at increased risk of breast cancer", "acronym": "IBIS-I", "hypothesis": "A study to evaluate the reduction in incidence of, and mortality from, breast cancer associated with taking tamoxifen daily for five years.", "primaryOutcome": "The development of histologically confirmed breast cancer, both invasive and non-invasive (i.e. including ductal carcinoma in situ [DCIS]", "secondaryOutcome": "Other cancers, other serious medical conditions or side effects", "intervention": "\n\tWomen were randomised to receive either tamoxifen 20 mg per day for 5 years or placebo\n\tDrug\n\tNot Applicable\n\tTamoxifen\n      ", "condition": "\n\tBreast cancer chemoprevention\n\tCancer\n\tBreast cancer\n      ", "studyDesign": "A multicentre randomized clinical trial of 7,000 women aged between 45 and 70 years who have a risk of breast cancer at least twice that of the general population", "overallEndDate": "2011-03-30T00:00:00.000Z", "clinicalTrialsGovNumber": "NCT00002644", "lastUpdated": "2026-08-05T13:57:17.88419963Z", "eligibility": {"inclusion": "To be eligible, women must satisfy at least one of the entry criteria listed below:\n1. A mammogram must have been taken within the last year indicating no malignant disease\n2. A signed consent form must have been obtained\n\nEntry criteria:\nThe entry criteria were based on a relative risk of at least twofold for women aged 45-70 years, fourfold for women aged 40-44 years and tenfold for women aged 35-39 years.\n\nAge 45-70 years:\n1. First-degree relative who developed breast cancer at age 50 years or less\n2. First-degree relative who developed bilateral breast cancer\n3. Two or more first or second-degree relatives who developed breast cancer\n4. Nulliparous and a first-degree relative who developed breast cancer\n5. Benign biopsy with proliferative disease and a first-degree relative who developed breast cancer\n6. Lobular carcinoma in situ\n7. Atypical ductal or lobular hyperplasia in a benign lesion\n8. Women at high risk who do not fit into the above categories (risk equivalent)*\n* These women must have clearly apparent family history indicating at least a twofold increased risk of breast cancer.\n\nAge 40-44 years:\n8. Two or more first or second-degree relatives who developed breast cancer at age 50 years or less\n9. First-degree relative with bilateral breast cancer who developed the first breast cancer at age 50 years or less\n10. Nulliparous and a first-degree relative who developed breast cancer at age 40 years or less\n11. Benign biopsy with proliferative disease and a first-degree relative who developed breast cancer at age 40 years or less\n12. Lobular carcinoma in situ\n13. Atypical ductal or lobular hyperplasia in a benign lesion\n14. Women at high risk who do not fit into the above categories (risk equivalent)*\n* These women must have clearly apparent family history indicating at least a fourfold increased risk of breast cancer.\n\nAge 35-39 years:\n15. Two or more first-degree relatives who developed breast cancer at age 50 years or less\n16. First-degree relative with bilateral breast cancer who developed the first breast cancer at age 40 years or less\n17. Lobular carcinoma in situ\n18. Women at high risk who do not fit into the above categories (risk equivalent)*\n*These women must have clearly apparent family history indicating at least a tenfold increased risk of breast cancer.", "exclusion": "1. Pregnant, or at pregnancy risk. If necessary, pre- and peri-menopausal women must use non-hormonal contraception during the trial\n2. Any previous cancer (except non-melanoma skin cancer or in situ cancer of the cervix)\n3. Life expectancy of less than 10 years or other medical condition more serious than the risk of breast cancer\n4. Psychologically and physically unsuitable for 5 years tamoxifen or placebo therapy\n5. Current treatment with anti-coagulants\n6. Previous deep vein thrombosis or pulmonary embolus\n7. Current tamoxifen use", "ageRange": "Mixed", "gender": "Female", "participantType": "Patient"}, "recruitment": {"recruitmentStart": "1992-04-14T00:00:00.000Z", "recruitmentEnd": "2011-03-30T00:00:00.000Z", "recruitmentStatusOverride": "", "recruitmentStartStatusOverride": "", "targetEnrolment": "7000", "totalFinalEnrolment": "7152"}, "countries": ["United Kingdom", "England", "Australia", "Belgium", "Finland", "Switzerland"], "locations": [{"name": "Wolfson Institute of Preventive Medicine", "city": "London", "state": "", "country": "England", "zip": "EC1M 6BQ"}], "sponsors": [{"organisation": "Queen Mary University of London (UK)", "sponsorType": "University/education", "rorId": "https://ror.org/026zzn846"}], "funders": [{"name": "Imperial Cancer Research Fund"}, {"name": "Cancer Research Campaign"}, {"name": "Cancer Research UK"}]}, "studySha256": "24166ac3423bd21e43f4a308fb350d86f1744a657234e856fe9aa7b67d3b14ad"}