An Extremely Rare Case of Thyroid Metastasis from Advanced Gastric Cancer.

Metastases to the thyroid area are extremely rare in cancer, more specifically, in gastric cancer, where intraperitoneal metastases are absent. Herein, we describe a case of a 41-year-old man who had advanced gastric cancer with metastasis to the right thyroid area, which was found 6 years after curative surgery. The patient presented with multiple enlarged right cervical lymph nodes and a right thyroid mass of 1.2 cm. We assumed that the patient had primary thyroid cancer as he had no signs of other metastases. We performed fine-needle cytology under ultrasonography on the thyroid nodule. However, with a positive carcinoembryonic antigen and a negative thyroid transcription factor 1 immunohistochemical staining results, the patient was diagnosed with metastatic adenocarcinoma that was of gastric origin. Subsequently, the patient was treated with radiotherapy and chemotherapy. This report aimed to raise the concern that gastric cancer may cause metastasis to the peri-thyroid area, involving the thyroid, parathyroid, and regional lymph nodes.