甲状腺転移性結腸腺癌：症例報告と文献レビュー

Colorectal adenocarcinoma is one of the most common malignancies worldwide. Although metastases typically affect the liver, lungs, and peritoneum, thyroid involvement is extremely rare, with fewer than 50 cases documented to date. We present the case of a 61-year-old woman with a history of sigmoid colon adenocarcinoma who subsequently developed a solitary pulmonary metastasis treated surgically. During follow-up, a suspicious thyroid nodule with cervical lymphadenopathy was detected. The patient underwent total thyroidectomy with lymph node dissection, and histopathological evaluation revealed a moderately differentiated adenocarcinoma. Immunohistochemistry demonstrated negativity for CK7 and TTF-1, with diffuse positivity for CDX2, CK20 and SATB2, confirming colorectal origin. Immunohistochemistry demonstrated negativity for CK7 and TTF-1, with diffuse positivity for CDX2, CK20 and SATB2, confirming colorectal origin. Additionally, we performed a literature review (2014-2025) and present a table summarizing 24 reported cases of thyroid metastases from colorectal adenocarcinoma. This case underscores the importance of considering thyroid metastasis in patients with colorectal cancer who present with thyroid nodules. Awareness of this rare manifestation and the use of immunohistochemical markers are essential to achieve an accurate diagnosis and to guide appropriate clinical management.