A Good Imitator of Medullary Thyroid Carcinoma: Thyroid Metastasis From a Neuroendocrine Tumor

ABSTRACT Objective To describe the diagnosis of a patient with thyroid metastasis from a bronchial carcinoid tumor, initially mistaken for a medullary thyroid carcinoma. Methods We present the clinical, laboratory, and imaging findings, along with a literature review. Results Typical bronchial carcinoids are well-differentiated neoplasms, which usually have a good prognosis. However, 15% of the cases may metastasize. This report describes the case of a 36-year-old woman with a history of a surgically removed bronchial carcinoid tumor, which did not relapse after a 4-year follow-up. Nine years later, the patient consulted for a thyroid nodule, and the anatomic pathology report showed a diagnosis of medullary thyroid carcinoma. Subsequently, immunohistochemistry showed that it was a thyroid metastasis from the bronchial carcinoid tumor, which completely changed the treatment and prognosis. Conclusion This case highlights the importance of adequate surgery, as well as a detailed review of the past medical history and a proper immunochemistry as part of the histopathologic examination. This will facilitate the distinction between medullary thyroid carcinomas and primary extrathyroid neuroendocrine tumors that have metastasized into the thyroid gland.