title: Occult medullary thyroid carcinoma. Unusual histologic variant presenting with metastatic disease.
abstract: A 66-year-old man presented with an enlarged cervical lymph node, interpreted on fine-needle aspiration as squamous cell carcinoma. Histologic assessment of the excised mass demonstrated a mucin-positive glandular neoplasm that, by immunohistochemistry, was positive for carcinoembryonic antigen, calcitonin, and neuron-specific enolase. A subsequent total thyroidectomy revealed a grossly normal organ with a 2-mm microscopic focus of medullary carcinoma and foci of C-cell hyperplasia in the immediate vicinity of the tumor. No amyloid could be demonstrated in either lesion. The diagnostic difficulty encountered in this case is related to the presence of a rare morphologic variant (devoid of amyloid and forming mucin-positive glands) occurring as an occult primary but presenting as a metastasis. Although an occult primary in medullary carcinoma is recognized in familial cases, such a phenomenon is rare in sporadic cases.
mesh_terms: D000368:Aged; D002116:Calcitonin / Q000032:analysis; D002272:Carcinoembryonic Antigen / Q000032:analysis; D002277:Carcinoma / Q000473:pathology*; D006801:Humans; D008207:Lymphatic Metastasis / Q000473:pathology; D008297:Male; D010751:Phosphopyruvate Hydratase / Q000032:analysis; D013964:Thyroid Neoplasms / Q000473:pathology*
chemical_list: D002272:Carcinoembryonic Antigen; D002116:Calcitonin; D010751:Phosphopyruvate Hydratase