A trial looking at tamoxifen or anastrozole in postmenopausal women with ductal carcinoma in situ of the breast (IBIS II DCIS)

Cancer type:

Breast cancer




Phase 3

This trial looked at 2 hormone therapy drugs called tamoxifen and anastrozole after surgery for ductal carcinoma in situ (DCIS). It was for women who had been through the menopause Open a glossary item and had oestrogen receptor positive Open a glossary item DCIS. This trial was supported by Cancer Research UK.

More about this trial

DCIS means the cells inside the ducts of the breast have started to turn into cancer cells. Some doctors refer to DCIS as a pre-cancerous condition. Others call it a very early form of breast cancer.

Doctors usually treat DCIS with surgery because if it is left untreated it may develop into invasive breast cancer.

In this trial doctors wanted to see if hormone therapy could help to lower the risk of DCIS or invasive breast cancer in women that have had surgery for DCIS. In this trial, some women had tamoxifen and some had anastrozole.

The aims of this trial were to

  • Find out if tamoxifen or anastrozole is better at stopping DCIS or invasive breast cancer coming back after surgery
  • Learn more about the side effects of tamoxifen and anastrazole

Summary of results

The trial team found that anastrozole was no better than tamoxifen in lowering the risk of the DCIS or invasive breast cancer coming back after surgery.

2, 980 women took part in this trial. Everyone had treatment for up to 5 years.

  • 1, 509 had tamoxifen and a dummy tablet (placebo Open a glossary item) of the other drug
  • 1, 471 had anastrozole and a dummy tablet of the other drug

After an average of 7 years, the trial team found that DCIS or invasive breast cancer had come back in 144 women. Of those,

  • 77 women had tamoxifen
  • 67 women had anastrozole

The researchers say this difference was not statistically significant Open a glossary item as it could have happened by chance.

The number of side effects the women in the 2 groups had was not different but the type of side effects the women reported were different.

Women who took tamoxifen had more

  • Gynaecological and skin cancers
  • Blood clots in the leg or lung
  • Hot flushes, vaginal bleeding and discharge

Women who took anastrozole had more

  • Fractures
  • Joint and muscle pain or stiffness  (musculoskeletal problems)
  • Strokes
  • Vaginal dryness

The trial team concluded that anastrozole was no better than tamoxifen at stopping DCIS or invasive breast cancer coming back after an average of 7 years of follow up. But anastrozole offers another treatment option for this group of women. The trial team will follow up these women for a longer period of time. They will release the next results when there is at least 10 years of follow up data available.

We have based this summary on information from the research team. The information they sent us has been reviewed by independent specialists (peer reviewed Open a glossary item) and published in a medical journal. The figures we quote above were provided by the trial team who did the research. We have not analysed the data ourselves.

Recruitment start:

Recruitment end:

How to join a clinical trial

Please note: In order to join a trial you will need to discuss it with your doctor, unless otherwise specified.

Please note - unless we state otherwise in the summary, you need to talk to your doctor about joining a trial.

Chief Investigator

Professor Jack Cuzick
Professor Antony Howell
Professor John Forbes

Supported by

Cancer Research UK
NIHR Clinical Research Network: Cancer
Queen Mary University of London

Other information

This is Cancer Research UK trial number CRUK/04/032/033.

Freephone 0808 800 4040

Last review date

CRUK internal database number:

Oracle 228

Please note - unless we state otherwise in the summary, you need to talk to your doctor about joining a trial.

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“I was keen to go on a clinical trial. I wanted to try new cancer treatments and hopefully help future generations.”

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