Metastatic colorectal carcinoma to the thyroid gland: A case report and literature review.

Although thyroid metastasis from colorectal carcinoma (CRC) is exceedingly rare, with a reported clinical incidence of ~0.1-0.3%, its detection typically signifies advanced-stage systemic disease. This atypical metastatic pattern generally correlates with a terminal stage and a historically poor prognosis, with a reported 5-year survival rate of <15%. A 78-year-old female presented with advanced sigmoid adenocarcinoma complicated by a thyroid mass that caused significant tracheal compression and was accompanied by multiple pulmonary metastases. The patient's initial clinical manifestations included chronic hematochezia and diarrhea. Given the patient's advanced age and poor baseline status, a palliative thyroidectomy was performed to alleviate acute airway obstruction, followed by levothyroxine replacement therapy. Postoperative histopathological examination and immunohistochemical profiling, including SATB2 and CK19 positivity together with PAX8 and TTF-1 negativity, supported a diagnosis of metastatic adenocarcinoma of colorectal origin. In conclusion, clinicians should maintain a low threshold of suspicion for secondary malignancies when evaluating new thyroid nodules in patients with a known history of CRC. Although the findings from a single case study have limited generalizability, this report underscores the potential value of multidisciplinary systemic staging and individualized palliative management in optimizing supportive care for patients with rare metastatic patterns.