aTTom Trial

Trial Overview and Summary

Chief Investigator: Professor Daniel Rea
Sponsor: University of Birmingham
Funders: Cancer Research UK (Trial No.CRUK/94/001)
Disease Site: Breast Cancer
Trial Type: Clinical Trial of an Investigational Medicinal Product 
Status: Follow-up
UKCRN Study ID: (if applicable) ISRCTN17222211
Open to new sites? No
Recruitment start date: 11/07/1991
Anticipated Recruitment end date 31/03/2005
CRCTU Trial Management Team: Late Phase Trial Management Team - B
Trial E-mail Address:

Tamoxifen is a drug that reduces the chance that breast cancer will return after breast cancer surgery. While there are newer drugs that may be even better than tamoxifen, they are not suitable for everyone and can have extra side effects. Tamoxifen is therefore still in widespread use and is saving thousands of lives world-wide.

In the early 1990, when the aTTom trial was developed, most patients received 2 to 5-years of tamoxifen and it was not known whether giving tamoxifen for longer was beneficial. The aTTom trial was designed to address this question. Women with early breast cancer who had received tamoxifen for a minimum of 2 years were randomised to STOP or CONTINUE. Those randomised to CONTINUE were asked to carry on taking tamoxifen for another 5-years. Information on patient diagnosis, treatment, survival and side effects were collected from the patients’ hospital and/or general practitioner and from the Office of National Statistics (under Section 251 exemption).

aTTom recruited 8863 women from 178 UK hospitals in the United Kingdom between July 1991 and March 2005 and follow up is on-going.

Please note that the trials team cannot give individuals clinical advice. Patients and their families should contact their treating physician to discuss trials for which they may be eligible.

Trial Protocol

A copy of the aTTom trial protocol can be found here: Protocol Version 3a_21-Aug-2000

Please note:  Clinical trial protocols are complex technical documents which should only be used for the treatment of subjects taking part in the trial.

Summary of Trial Results

The preliminary results of the trial were presented at the American Society of Clinical Oncology (Journal of Clinical Oncology 31, No.18 Suppl (June 2013): 5-5) and the European Society for Medical Oncology (European Journal of Cancer 49, Suppl 2, S1-S1028) in 2013. The result demonstrated an improvement in disease-free survival although the risk of endometrial cancer was increased slightly.

A lay summary of the results is available on the Cancer Research UK website

Information for Patients Who Took Part in the aTTom Trial

A patient summary and information about how to withdraw your consent for further processing of your data or the collection of tissue samples as part of the aTTom-Extended trial can be found here:

aTTom and aTTom-Extended Patient Summary