• Naruhito Takido, Ryusuke Saito, Kaoru Okada, Norifumi Kanai, Yoshihiro Shono, Hiroaki Mitsugashira, Muneyuki Matsumura, Kengo Sasaki, Koji Miyazawa, Atsushi Fujio, Kazuaki Tokodai, Keigo Murakami, Hironobu Sasano, Michiaki Unno, Takanori Ishida, and Takashi Kamei.
• Department of Surgery, Tohoku University Graduate School of Medicine.
• Tohoku J. Exp. Med. 2023 Sep 20; 261 (1): 758175-81.

AbstractTumor-to-tumor metastasis is a rare phenomenon in which primary tumor cells metastasize to other tumors. Herein, we report an extremely rare case of tumor-to-tumor metastasis of medullary thyroid carcinoma to a paraganglioma in a patient with multiple endocrine neoplasia type 2B. Based on genetic examination, a 36-year-old woman was diagnosed with multiple endocrine neoplasia type 2B when she was 24 years old. She had a history of total thyroidectomy for medullary thyroid carcinoma and bilateral adrenalectomy for pheochromocytomas, which were performed when she was 15 years and 29 years old, respectively. Follow-up computed tomography demonstrated a retroperitoneal tumor of 30 mm in diameter beside the left kidney and a liver tumor of 16 mm in diameter located in segment 6. The retroperitoneal and liver tumors were surgically resected and examined by a pathologist. Histological examination revealed the classic Zellballen pattern in the retroperitoneal tumor, rendering the diagnosis of a paraganglioma recurrence. Inside the tumor, a white nodule positive for carcinoembryonic antigen, weakly positive for calcitonin, and negative for tyrosine hydroxylase, was identified and diagnosed as a metastatic medullary thyroid carcinoma with high malignant potential. The liver lesion was diagnosed as a metastasis of the medullary thyroid carcinoma. This is the first report of tumor-to-tumor metastasis of medullary thyroid carcinoma to paraganglioma in a patient with multiple endocrine neoplasia type 2B twenty years after total thyroidectomy.

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