Medullary Thyroid Carcinoma Metastatic to the Breast: Case Report

Aims: To spot the light on metastatic tumors to the breast which represent only 0.5-1.5% of breast malignancies to avoid misdiagnosis as primary breast tumors. Presentation of the Case: 45-year-old female was referred to the Oncology Department of Meet Ghmmr Oncology Center in November 2017 after total thyroidectomy followed by cervical lymph node dissection for medullary thyroid carcinoma (MTC) 1 year ago at Oncology Center Mansoura University. The panel recommended postoperative radiotherapy. One month after the end of radiotherapy, she complained of frequent headache attacks and abdominal pain. CT was done in February 2018 revealed metastasis to the brain, lung, liver and ovaries. After the fifth cycle of chemotherapy, a progressively enlarging left breast mass appeared, that proved to be metastatic MTC. Discussion: MTC is a neuroendocrine tumor of the thyroid gland. Breast is an unusual metastatic site for MTC. Consequently, breast masses should be evaluated with caution, especially in the presence of a known primary malignancy. Histopathologic examination is the key diagnostic tool. Conclusion: Metastasis to the breast should be considered in the differential diagnosis of a breast mass in a patient with a past history of MTC. Histopathologic examination and proper panel of immunohistochemical markers are fundamental for diagnosis to prevent unneeded surgery.