Use of the levonorgestrel-releasing intrauterine system in breast cancer patients.

OBJECTIVE: To study the recurrence of breast cancer among patients who were using the levonorgestrel-releasing intrauterine system (LNG IUS).
DESIGN: A retrospective, controlled cohort analysis.
SETTING: Six Belgian hospitals. PATIENT(S): We identified 79 breast cancer patients who used the LNG IUS, and we selected a control group of 120 patients with no history of LNG IUS use and who were closely matched for age at diagnosis, tumor stage, tumor grade, and treatment modalities. Two subgroups were identified: [1] breast cancer patients who continued using the LNG IUS after diagnosis and [2] breast cancer patients who began using an LNG IUS after treatment for breast cancer. INTERVENTION(S): Patient's data were collected and survival analysis was performed. MAIN OUTCOME MEASURE(S): Breast cancer recurrence rate. RESULT(S): There was a recurrence rate of 21.5% (17/79) among LNG IUS users and of 16.6% (20/120) among the control group (adjusted hazard ratio, 1.86; 95% confidence interval, 0.86-4.00; no statistically significant difference). Subgroup analysis showed that women using the LNG IUS (n = 38) at the time of breast cancer diagnosis (and who continued its use) had a statistically significantly increased risk of recurrence (adjusted hazard ratio, 3.39; 95% confidence interval, 1.01-11.35) compared with patients in the control group. There was 47.4% (18/38) nodal involvement in this subgroup, and all patients who recurred had metastatic disease. CONCLUSION(S): Overall, we did not find an increased risk of breast cancer recurrence associated with use of the LNG-IUS. However, in a subgroup analysis of women who developed breast cancer while using an LNG IUS and who continued to use the LNG IUS, we found a higher risk of recurrence of borderline statistical significance. Additional research is needed to confirm or refute these findings.