ODP585 Occult metastatic medullary thyroid carcinoma without detectable primary tumor

Background Occult thyroid cancer is a particularly rare type of thyroid carcinomas. The absolute majority is presented by papillary thyroid carcinoma. We report a case of a medullary thyroid carcinoma (MTC) that was detected as a primary tumor neither on preoperative ultrasound examination nor on postoperative morphological examination. Case A 57-year-old patient with no personal or family history of thyroid disease presented to the surgeon with the complaint of swelling in the cervical lymph nodes. Ultrasonography of the thyroid showed a hypoechoic 4 mm zone with peripheral calcification in the right lobe and two suspicious malignant lymph nodes 14×12 mm and 10×7 mm in the right paratracheal region. A blood test revealed no abnormalities in thyroid function (TSH 0.9 mUI/L, fT3 4.25 pmol/l, fT4 10.2 pmol/l). However, the calcitonin (CT) and the carcinoembryonic antigen (CEA) levels were significantly elevated – 144 pg/ml (N for male Conclusion Metastatic medullary thyroid carcinoma without detectable primary tumor is a rare but real occurrence that might be encountered in practice. The lack of malignant findings in the thyroid gland during preoperative examination complicates the diagnostic. Presentation: No date and time listed