Colorectal cancer metastasis to the thyroid: A case report and review of the literature.

Metastatic thyroid cancer is rare. Here, the case of a patient with colon cancer that metastasized to the thyroid is described. The patient underwent radical rectal cancer surgery in August 2017 and received six cycles of chemotherapy with oxaliplatin and capecitabine postoperatively. On August 4, 2018, the patient was admitted to the hospital due to the discovery of thyroid nodules on ultrasound and carcinoembryonic antigen levels within the normal range. The biopsy from the fine needle aspiration suggested a malignant tumor. The patient underwent radical thyroid cancer surgery. Using intraoperative rapid frozen pathology, medullary carcinoma was diagnosed. Using postoperative routine pathology combined with immunohistochemistry results, thyroid metastasis from colorectal adenocarcinoma was diagnosed. After surgery, the patient regularly visited the outpatient clinic for chemotherapy with capecitabine. As of May 2023, the patient is still alive with no recurrence.