In study published in the 17 November Lancet, doctors in Leicester have found that the hormone-releasing intrauterine device (IUD, or coil), Mirena, can stop potentially dangerous changes to the lining of the womb in women taking tamoxifen.
Thousands of women take tamoxifen after a diagnosis of breast cancer because of its success in preventing recurrence of the disease.
But one of the unwanted side effects of the drug is polyps and fibroids in the womb and thickening of the endometrium as well as a two to threefold increase in endometrial cancer.
Bleeding associated with benign changes in the womb need investigating to make sure that it is not caused by cancer.
But the research team from the University of Leicester say that use of Mirena can significantly reduce these changes in the womb.
While tamoxifen blocks the effect of the hormone estrogen on breast tissue, it leads to polyps in the uterus in nearly one in three women taking it and thickening of the uterine lining in two thirds.
However, the protective effects against breast cancer outweigh the small increase in the number of uterus cancers it causes.
Mirena works by releasing a small amount of the hormone progestagen into the uterus and is used as a contraceptive.
In the Leicester trial, 122 postmenopausal women taking tamoxifen were assigned either to a group which had the device fitted or a group which received surveillance only.
Dr Francis Gardner and his team found that women with the IUD had no new polyps after one year and 13% less fibroids than women without the device.
One side-effect of Mirena was the increased likelihood of more vaginal bleeding in the first few months after its insertion, though this generally settled down.
"This study provides preliminary evidence of a novel treatment which could lead to the improvement of health care of thousands of women taking tamoxifen as adjuvant treatment for breast cancer," said Dr Gardner.
Writing in the Lancet, the researchers have called for a larger study to confirm their findings.
Cancer Research Campaign head of clinical programmes, Kate Law said that, while the study was interesting, a number of women could be put off by the additional bleeding the IUD caused.
And she added: " We are now seeing the second and third generation of tamoxifen come through with fewer side effects.
"It may be by the time there is a trial involving thousands of women these side effects are no longer so much of a problem."