Metastatic medullary thyroid carcinoma in sputum. A light and electron microscopic study.

Medullary thyroid carcinoma (MTC) was diagnosed in a 43-year-old male by light microscopy, electron microscopy and immunohistochemistry. Five years after thyroidectomy, malignant cells with the typical cytologic and electron microscopic features of MTC were seen in his sputum, and extensive pulmonary metastases from MTC were subsequently documented at autopsy. Sputum examination is a useful diagnostic technique in patients with MTC in whom pulmonary metastases are suspected.