The levonorgestrel-releasing intrauterine system (Mirena) may prevent endometrial changes induced by tamoxifen, according to researchers from the University of Leicester.
Tamoxifen, used as an adjuvant treatment for breast cancer, frequently causes episodes of bleeding, which could be associated with proliferative changes to the endometrium or with endometrial cancer, Dr Francis Gardner (department of obstetrics and gynaecology) and colleagues say.
The researchers randomised 113 women, who were taking tamoxifen for breast cancer, into two groups — one group underwent endometrial surveillance alone, while those in the other group were monitored before and after insertion of the intrauterine system. Endometrial samples from women in the control group (no intrauterine system fitted) remained unchanged throughout the 12-month study period, while women who had had the system fitted had a characteristic decidual change to the endometrium. There was also a significant difference in the incidence of polyp formation, which supported the role of the device in preventing endometrial polyps, the researchers say.
The only significant adverse effect of the system was vaginal bleeding. Dr Gardner et al comment: "Although the levonorgestrel-releasing intrauterine device has a protective action against the uterine effects of tamoxifen, it causes more vaginal bleeding episodes after insertion but the uniform decidualisation of the endometrium should be regarded as very reassuring in clinical practice." (Lancet 2000;356:1711) Mirena is licensed for contraceptive use only.