The incidence of thyroid cancer has been increasing in Japan. The major histological type of thyroid cancer is papillary thyroid carcinoma (PTC) which is derived from follicular cells, whereas medullary thyroid carcinoma (MTC) is rarer and derived from the para-follicular C-cells. Concurrent occurrence of these two different types of thyroid cancer is extremely rare and a precise diagnosis is difficult in such cases. Herein, we report a rare patient with co-occurrence of PTC and MTC.
A 55-year-old Japanese woman with no significant family medical history was referred to our hospital with a thyroid nodule that had been detected incidentally. She had a history of hypertension and type 2 diabetes as comorbidities. Two nodules could be detected by CT; one nodule was diagnosed as an adenomatous goiter and the other as a PTC by fine needle aspiration cytology. No other tumor could be detected before treatment. We performed total thyroidectomy, because the PTC was located in the thyroid isthmus. In the final pathological diagnosis, the two tumors were confirmed as adenomatous goiter and PTC. In addition, small MTC tumors were also detected in both the right and left lobes of the thyroid gland, that had not been detected before the surgery. There was no evidence of either pheochromocytoma or hyperparathyroidism, and the patient refused to provide consent for RET gene mutation analysis. Therefore the MTC was diagnosed as being sporadic.
In this case, preoperative diagnosis of the MTC tumors by imaging could not be made, because the tumors were too small to detect by imaging. Measurement of the serum calcitonin and serum carcinoembryonic antigen levels may have been useful, however, no guidelines recommend measurement of these parameters for patients diagnosed as having PTC. To avoid inadequate treatment because of missed diagnosis of MTC, as in this case, a more effective diagnostic approach is expected.
