An international multicentre study of tamoxifen versus placebo in women at increased risk of breast cancer

ISRCTN	ISRCTN91879928
DOI	https://doi.org/10.1186/ISRCTN91879928
ClinicalTrials.gov (NCT)	NCT00002644
Clinical Trials Information System (CTIS)	2005-003091-38
Protocol serial number	N/A
Sponsor	Queen Mary University of London (UK)
Funders	Imperial Cancer Research Fund, Cancer Research Campaign, Cancer Research UK

Submission date: 24/02/2006
Registration date: 01/06/2006
Last edited: 24/04/2025

Recruitment status: No longer recruiting
Overall study status: Completed
Condition category: Cancer

Prospectively registered

Protocol

Statistical analysis plan

Results

Individual participant data

Plain English summary of protocol

https://www.ibis-trials.org/thetrials/ibistrials/ibis-1

Contact information

Prof Jack Cuzick
Scientific

Centre for Cancer Prevention
Wolfson Institute of Preventive Medicine
Charterhouse House Square
London
EC1M 6BQ
United Kingdom

Phone	+44 (0)207 882 5973
Email	j.cuzick@qmul.ac.uk

Miss Joanna Zahedi
Scientific

Project Manager/Data Manager
Barts CTU
Centre for Evaluation and Methods
Wolfson Institute of Population Health
Faculty of Medicine and Dentistry
Queen Mary University of London
London
E1 4NS
United Kingdom

Email	j.zahedi@qmul.ac.uk

Study information

Primary study design	Interventional
Study design	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
Secondary study design	Randomised controlled trial
Study type	Participant information sheet
Scientific title	An international multicentre study of tamoxifen versus placebo in women at increased risk of breast cancer
Study acronym	IBIS-I
Study objectives	A study to evaluate the reduction in incidence of, and mortality from, breast cancer associated with taking tamoxifen daily for five years.
Ethics approval(s)	The start of the IBIS I study predated the existence of Multicentre Research Ethics Committees (MREC). However, Central Office for Research Ethics Committees (COREC) have appointed the Central and South Bristol Research Ethics Committee to be the lead REC for the IBIS I study. The Central South Bristol REC reference assigned to study is E3244.
Health condition(s) or problem(s) studied	Breast cancer chemoprevention
Intervention	Women were randomised to receive either tamoxifen 20 mg per day for 5 years or placebo
Intervention type	Drug
Phase	Not Applicable
Drug / device / biological / vaccine name(s)	Tamoxifen
Primary outcome measure(s)	The development of histologically confirmed breast cancer, both invasive and non-invasive (i.e. including ductal carcinoma in situ [DCIS]
Key secondary outcome measure(s)	Other cancers, other serious medical conditions or side effects
Completion date	30/03/2011

Eligibility

Participant type(s)	Patient
Age group	Adult
Lower age limit	35 Years
Upper age limit	70 Years
Sex	Female
Target sample size at registration	7000
Total final enrolment	7152
Key inclusion criteria	To be eligible, women must satisfy at least one of the entry criteria listed below: 1. A mammogram must have been taken within the last year indicating no malignant disease 2. A signed consent form must have been obtained Entry criteria: The 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. Age 45-70 years: 1. First-degree relative who developed breast cancer at age 50 years or less 2. First-degree relative who developed bilateral breast cancer 3. Two or more first or second-degree relatives who developed breast cancer 4. Nulliparous and a first-degree relative who developed breast cancer 5. Benign biopsy with proliferative disease and a first-degree relative who developed breast cancer 6. Lobular carcinoma in situ 7. Atypical ductal or lobular hyperplasia in a benign lesion 8. Women at high risk who do not fit into the above categories (risk equivalent)* * These women must have clearly apparent family history indicating at least a twofold increased risk of breast cancer. Age 40-44 years: 8. Two or more first or second-degree relatives who developed breast cancer at age 50 years or less 9. First-degree relative with bilateral breast cancer who developed the first breast cancer at age 50 years or less 10. Nulliparous and a first-degree relative who developed breast cancer at age 40 years or less 11. Benign biopsy with proliferative disease and a first-degree relative who developed breast cancer at age 40 years or less 12. Lobular carcinoma in situ 13. Atypical ductal or lobular hyperplasia in a benign lesion 14. Women at high risk who do not fit into the above categories (risk equivalent)* * These women must have clearly apparent family history indicating at least a fourfold increased risk of breast cancer. Age 35-39 years: 15. Two or more first-degree relatives who developed breast cancer at age 50 years or less 16. First-degree relative with bilateral breast cancer who developed the first breast cancer at age 40 years or less 17. Lobular carcinoma in situ 18. Women at high risk who do not fit into the above categories (risk equivalent)* *These women must have clearly apparent family history indicating at least a tenfold increased risk of breast cancer.
Key exclusion criteria	1. Pregnant, or at pregnancy risk. If necessary, pre- and peri-menopausal women must use non-hormonal contraception during the trial 2. Any previous cancer (except non-melanoma skin cancer or in situ cancer of the cervix) 3. Life expectancy of less than 10 years or other medical condition more serious than the risk of breast cancer 4. Psychologically and physically unsuitable for 5 years tamoxifen or placebo therapy 5. Current treatment with anti-coagulants 6. Previous deep vein thrombosis or pulmonary embolus 7. Current tamoxifen use
Date of first enrolment	14/04/1992
Date of final enrolment	30/03/2011

Locations

Countries of recruitment

United Kingdom
England
Australia
Belgium
Finland
Switzerland

Study participating centre

Wolfson Institute of Preventive Medicine

London
EC1M 6BQ
United Kingdom

Results and Publications

Individual participant data (IPD) Intention to share	No
IPD sharing plan summary	Not provided at time of registration
IPD sharing plan

Study outputs

Output type	Details	Date created	Date added	Peer reviewed?	Patient-facing?
Results article	results	14/09/2002		Yes	No
Results article	results	01/02/2003		Yes	No
Results article	results	21/04/2004		Yes	No
Results article	results	20/08/2006		Yes	No
Results article	results	21/02/2007		Yes	No
Results article	results	15/12/2009		Yes	No
Results article	results	04/05/2011		Yes	No
Results article	results	01/07/2012		Yes	No
Results article	substudy results	01/01/2013		Yes	No
Results article	placebo arm results	08/10/2014		Yes	No
Results article	extended long-term follow-up results	01/01/2015		Yes	No
Results article	results	01/08/2016		Yes	No
Results article	results	01/03/2017		Yes	No
Results article	results	10/08/2017		Yes	No
Results article	results	03/03/2021	04/03/2021	Yes	No
Participant information sheet	Participant information sheet	11/11/2025	11/11/2025	No	Yes
Study website	Study website	11/11/2025	11/11/2025	No	Yes

Editorial Notes

24/04/2025: Contact details updated, total final enrolment added.
04/03/2021: Publication reference added.
25/02/2019: Publication references added.
13/02/2019: The following changes were made to the trial record:
1. A EudraCT number and a ClinicalTrials.gov number were added.
2. The plain English summary was updated.
3. The sponsor contact details were updated.
4. The participant information sheet link was updated.