Breast Uptake of Radioiodine in Non-breastfeeding Women

We show 2 cases of breast uptake of radioiodine in non-breastfeeding women. A 40-year-old female patient with papillary thyroid carcinoma referred to nuclear medicine department for radioiodine ablation. Post radioiodine whole body scan revealed bilateral uptake at the upper thoracic region. Single photon emission computed tomography/computed tomography (SPECT/CT) confirmed symmetrical mammary gland uptake at both breasts. The patient had a pituitary microadenoma and hyperprolactinemia but she had suspended the treatment looking for pregnancy. We also show another case of a 41-year-old female patient with papillary thyroid carcinoma and extrathyroidal disease, without history of breast cancer, mastitis, hyperprolactinemia, or galactorrhea, also showing symmetrical mammary gland uptake at body scan. These cases exemplify that radioiodine uptake is not specific for thyroid tissue. It can also be seen in healthy non-thyroidal tissue, including breast, or in benign and malignant non-thyroidal tumors, which could be mistaken for thyroid cancer. Despite breast uptake of radioiodine is a common finding in postpartum or lactating women, it is important to correctly evaluate the breast radioiodine uptake and differentiate it from lung or axillary metastatic foci of thyroid cancer. In breast the radioiodine uptake is dependent of the expression of NIS (Sodium iodide symporter). The functional NIS expression in breast is the most important mechanism of breast uptake. SPECT/CT is useful in the differentiation of benign breast uptake with lung metastases or axillary metastases of thyroid cancer.