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

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 ) 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 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 ) 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.