Clinical observation of metastatic thyroid disease in a patient with breast cancer

Metastatic tumors of the thyroid gland (TG) are rare. Usually thyroid gland metastases originate from renal, lung, skin and gastrointestinal cancers. Breast cancer metastases are more rare and in various samples amount to 3 to 34% of all cases of the metastatic thyroid disease. We present a rare case of metastatic carcinomatosis into the thyroid goiter in a 63-year old female patient who has received combination therapy for breast cancer. In 2016, right-sided mastectomy was performed due to the right breast cancer (invasive carcinoma, non-specific type, Grade 2, with skin invasion) with subsequent four chemotherapy courses. A slowly growing nodule in the thyroid gland was first found in 2012; in 2017, fine needle aspiration biopsy was performed, which showed a follicular tumor that resulted in thyroidectomy. At the histological examination, against the background of thyroid goiter, multiple small lesions with advanced nuclear polymorphism were found, with doubtful diagnosis. To clarify the histogenesis of the tumor lesions, immunohistochemical assessment was performed. Its first phase included the markers of primary thyroid tumors (thyroglobulin, TTF-1), and the second one consisted of the breast cancer diagnostic panel (mammoglobin, GATA-3, estrogen and progesterone receptors). The results showed multiple small metastases of the invasive breast carcinoma of non-specific type into the thyroid goiter. Taking into account eventual problems of differential diagnosis and significant morphological polymorphism of thyroid tumors, we recommend extending of the immunohistochemistry panel in this patient category.