Radioactive Iodine Therapy Did Not Significantly Increase the Incidence and Recurrence of Subsequent Breast Cancer.

Abstract

Previous studies on the extent to which radioactive iodine (RAI) therapy for thyroid cancer increases the risk of subsequently developing breast cancer have given conflicting results. This study aimed to evaluate the effect of RAI treatment on breast cancer development and recurrence among female patients with primary thyroid cancer. This was a retrospective cohort study. The risk of subsequent breast cancer associated with RAI and its dose in hazard ratios (HRs) with 95% confidential intervals (CIs) were calculated using time-dependent Cox proportional hazard models. A total of 6150 patients with thyroid cancer enrolled between 1973 and 2009 were followed until December 2012. Of these, 3631 (59.0%) received RAI therapy. During the follow-up period, 99 primary breast cancers were diagnosed. Risk of breast cancer development according to RAI therapy and RAI dose during treatment for primary thyroid cancer. RAI therapy did not significantly increase the incidence of subsequent breast cancer among female patients (hazard ratio [HR], 0.49; 95% confidence interval [CI], 0.22-1.06) when a 2-year latency period was accounted for. High-dose RAI (≥120 mCi) was associated with a reduced incidence of subsequent breast cancer (HR, 0.17; 95% CI, 0.05-0.62) in the cohort with a 2-year latency period. The long-term follow-up results of this study suggest that RAI treatment for patients with thyroid cancer may not increase the risk or recurrence of breast cancer.