A Case of Solitary Thyroid Metastasis from Adenocarcinoma of the Descending Colon

Among surgical cases of malignant thyroid tumors, metastatic tumors are rare. The most common primary sites for metastatic thyroid tumors are the kidney, lung, and breast, and metastasis from colon cancer is quite rare. In this study, we report a rare case of a 65-year-old man who was diagnosed as having a thyroid metastasis after surgery for colon cancer. One year after undergoing partial colon resection and combined diaphragmatic resection for colon cancer at our department of surgery, he was referred to our department because of an enlarged mass in the right lobe of the thyroid gland noted on a CT scan. Three months after his initial visit to our department, we performed right lobe thyroidectomy + D1 dissection. Postoperative histopathological examination revealed moderately differentiated adenocarcinoma, and we made the diagnosis of thyroid metastasis from colorectal cancer. One month after the thyroid surgery, the patient was initiated on treatment with 8 courses of mFOLFOX6 + panitumumab therapy administered once every 3 weeks. Until now, 2 years and 2 months since the thyroid surgery, the patient has shown no evidence of recurrence. There have been only 27 case reports of thyroid metastasis from colorectal cancer in Japan. There is still no consensus on whether surgery should be recommended or not. Many reports indicate that surgery is the treatment of first choice when the primary tumor is under control and resectable and there are no synchronous metastases in other organs. Chemotherapy is selected as the treatment of first choice in many cases. The number of chemotherapy regimens for colorectal cancer has been increasing in recent years, and we hope that the prognosis of patients with thyroid metastases from colorectal cancer will also improve further in the future. It may be necessary to recognize the possibility of thyroid metastasis as well as primary thyroid cancer in patients with a history of colorectal cancer.