SAT530 Use of Tamoxifen and Cabergoline to Suppress Breast Tissue Uptake of Radioactive Iodine Among Differentiated Thyroid Cancer Patients

Disclosure: A.H. Mohamed: None. M. Basina: None. Background: Radioactive iodine (RAI) has been used in thyroid cancer treatment. Physiologic breast tissue uptake and accumulation of RAI are not desirable due to increased carcinogenesis risk. Case1:31 years old non lactating female diagnosed with stage IVB papillary thyroid cancer and underwent total thyroidectomy and bilateral neck dissection. She had high initial risk with stage of T3N1bM1 and underwent 118 mCi of I-131 treatment with pulmonary foci. One year later, she had biochemical and structural incomplete response and underwent I-123 RAI uptake scan demonstrating residual disease in the right neck and diffuse breast uptake, thus, I-131 treatment was deferred. The patient was started on cabergoline 0.5 mg daily for 2 months. Repeated I-123 uptake scan during day 2 of Cabergoline remained with diffuse breast uptake. Four months later, another repeated RAI uptake scan after 4 months showed minimal breast uptake and RAI I-131 treatment was given. She had normal mammogram screening. Case2: 41 years old non lactating female diagnosed with stage II papillary thyroid cancer and underwent total thyroidectomy with right neck dissection. She had moderate initial risk with stage of T3 N1aM0 and underwent 159 mCI of I-131 treatment. Two years later, she had structural incomplete response and repeated I-123 uptake scan showed thyroid bed foci of avid uptake and diffuse bilateral breast uptake, thus, I-131 therapy was deferred. The patient was started on cabergoline 0.25 mg daily for 4 weeks and Tamoxifen 10 mg twice daily for 10 days prior to repeated I-123 RAI scan that redemonstrated thyroid bed foci without breast tissue uptake. She had normal mammogram screening. DiscussionPotential malignancy risk secondary to non-thyroidal RAI accumulation in tissues was reported. The mechanism of breast RAI uptake involves Na/iodide symporter channel regulated by prolactin and estrogen. Blocking the effect of these hormones prior to I-131 administration are believed to prevent breast uptake. We describe two papillary thyroid cancer cases with breast RAI uptake that was suppressed partially with Cabergoline (prolactin lowering agent) and fully with combination of Cabergoline and Tamoxifen (estrogen receptor blocker). Further studies are needed to evaluate the efficacy of Tamoxifen and cabergoline in suppressing physiologic breast RAI uptake. Presentation Date: Saturday, June 17, 2023