Unusual case of metastatic thyroid nodule: nonpalpable breast mass as origin

To document a case of thyroid cancer metastatic from the breast. We present the clinical, laboratory, radiologic, and biopsy findings in our patient and review the related literature. A 47-year-old female patient was referred to our clinic because of dyspnea and generalized bone pain. Physical examination revealed a diffusely enlarged nodular goiter, and fine-needle aspiration biopsy demonstrated intrathyroidal anaplastic cells. Total thyroidectomy was done, and the histopathologic diagnosis was anaplastic carcinoma. Unexpected rapid progression of the disease with cervical and intrathoracic lymphadenopathies and osteoblastic metastatic lesions without radioiodine uptake prompted us to attempt to rule out a primary nonthyroidal malignant lesion metastatic to the thyroid gland. The plasma level of CA 15-3 was profoundly increased (388 U/mL). Detailed reassessment of the patient disclosed a small mass in the right mammary gland with histopathologic features similar to those of the thyroidectomy material. Reevaluation of the thyroid specimens resulted in a final diagnosis of primary breast carcinoma in conjunction with metastatic carcinoma of the thyroid. Thorough systemic clinical assessment of a patient with a thyroid nodule and careful study of biopsy specimens should be done to ascertain whether the nodule is a primary or a metastatic lesion.