Overall Cancer Risk Lower, But Don't Skip Mammograms if You Have A Progesterone IUD

Determining one's cancer risk from hormone exposure is difficult as hormones both protect against and cause cancer. A levonorgestrel-releasing intrauterine device (IUD) like Mirena or Skyla may protect users against cancers of the endometrium, ovary, pancreas, and lung, but increase their risk for breast cancer, according to a new study by Tuuli Soini, MD, from the Department of Obstetrics and Gynecology, Hyvinkää Hospital, Finland, and colleagues write in an article published in the August issue of Obstetrics & Gynecology.
Among women in Finland, Dr. Soini and coauthors analyzed data on all Finnish women between 30 and 49 years of age who were reimbursed for the levonorgestrel-releasing IUD between 1994 and 2007 for the treatment of  heavy menstrual bleeding or menorrhagia.  The breast cancer incidence among users of the hormone-releasing IUD was 7% higher than expected compared with women who did not use the IUD, with an excess of 188 cases. Among women who had  at least 2 IUDs, there was an excess of 76 cases, for an increase of 20%.
However the levonorgesterel IUDs can protect against cancer also. Compared with the general population, the standardized incidence ratio for endometrial adenocarcinoma after at least 1 levonorgestrel-releasing IUD  the risk is half as great, and the risk of ovarian cancer was also reduced by almost half.Even lung and pancreatic cancers were reduced in the IUD users.
The risk of breast cancer after at least 1 purchase was almost 20% greater, and even lightly higher if the IUD had been used for at least 5 years. 

This research was supported by research grants from Helsinki University Hospital and Hyvinkää Hospital. The authors have disclosed no relevant financial relationships.
Obstet Gynecol. 2014;124:292-299.

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