FOLLICULAR VARIANT OF PAPILLARY THYROID CARCINOMA AND MEDULLARY THYROID MICROCARCINOMA OCCURRING SIMULTANEOUSLY IN THE THYROID: A RARE CASE

Background Follicular variant of papillary thyroid carcinoma (FV-PTC) is a variant that develops from follicular cells, showing the nuclear properties of papillary thyroid carcinoma. Medullary thyroid carcinoma (MTC) is a malignant neuroendocrine tumor that develops from parafollicular C cells. It is more common in the fifth to sixth decades and in women. MTC smaller than 10 mm is referred to as medullary thyroid microcarcinoma (microMTC). Case A 59-year-old female patient with follow-up due to multinodular goiter underwent total thyroidectomy. Macroscopically, a 3.6 × 2 cm encapsulated solid nodular lesion in the right lobe and smaller nodular lesions in all thyroid material were observed. Microscopically, a tumor with capsular invasion had a follicular pattern of cells containing nuclear enlargement, nuclear crowding, nuclear overlapping, nuclear clearing, and nuclear groove on the background of multinodular goiter in the right lobe. In a separate focus at a distance of 1 mm from the tumor, a 5-mm infiltrative lesion of cell groups with eosinophilic sitoplasma containing polygonal, oval and elongated hyperchromatic nucleus with nucleoli in a stromal amyloid material was observed. Immunohistochemically, there was focal positive CK19 and luminal positive HBME-1 staining in the first lesion. Galectin-3 was negative. In the second lesion, positive calcitonin and CEA staining were striking. The first lesion as FV-PTC and the second lesion as microMTC were reported. Conclusions It is very rare to see synchronized occurrence of FV-PTC and microMTC originating from different cells as 2 different primers in the same thyroid lobe. Whether the occurrence is coincidental or by common mutation remains a mystery today.