Breast levonorgestrel concentrations in women using a levonorgestrel-releasing intrauterine system

To measure breast tissue and serum LNG concentrations in women using a LNG-IUS.

This pilot study was performed in 25 healthy women undergoing breast surgery at the Ghent University hospital. LNG concentrations were measured in serum and microdissected breast tissue samples using a validated ultra-performance liquid chromatography/tandem mass spectrometry assay.

The mean LNG concentration in the 18 LNG-IUS users was 0.18±0.16 ng/mL in serum and 0.26±0.28 ng/g in breast tissue. For four women without any form of hormonal contraceptive (the negative controls), the mean concentrations were below the limit of quantification, i.e., 0.15 ng/mL and 0.20 ng/g, for serum and breast tissue, respectively. For the three positive controls the concentrations in the serum (20.5 and 3.4 ng/ml) and the breast (3.74 and 1.24 ng/g) were respectively for the 20 μg EE/100 μg users and 315 pg/ml in the serum and 1.17 ng/g in the breast for the minipill user. The intracellular free fraction of LNG may be as low as 0.008 ng/g.

The concentration of LNG in breast epithelium cells in women using the LNG-IUS is very low.

The relationship between the serum and breast tissue levels of LNG was studied in women using a LNG-IUS or oral LNG-containing contraception. Compared to oral contraception, the tissue levels of LNG in LNG-IUS users are much lower in the breast. It is not known what level of LNG exposure in the breast would stimulate RANKL and WNT4 expression; such information is needed.