Simultaneously occurring liver metastases of pheochromocytoma and medullary thyroid carcinoma - A diagnostic pitfall with clinical implications for patients with Multiple Endocrine Neoplasia Type 2a

Malignant pheochromocytoma is an exceptional complication in patients with Multiple Endocrine Neoplasia Type 2a (MEN2a). In this paper; we report on a 53-year-old male patient with an evident RET gene germline mutation, who s imultaneously developed hepatic metastases of medullary thyroid carcinoma ( MTC) and pheochromocytoma. Comprehensive immunohistochemical investigations were performed to elaborat e markers which could be useful for differentiating between MTC metastases and pheochromocytoma, respectively. Calcitonin and CEA, in particular cytokeratins and trefoil factor family 1 (TFF1), were detectable exclusively in MTC, whereas all the other markers r evealed a comparable expression in both MTC and pheochromocytoma. The only clues that could indicate a potential malignant course were size, a lack of sustentacular cells and hyaline globules, and a focal spindle cell pattern in pheochromocytoma. Owing to a wide agreement in cellular differentiation and a lack of specifi c, routinely applicable markers for pheochromocytomas, a comprehensive and goal-directed immunohistochemistry is required to rule out pheochromocytoma metastasis in patients with MEN2a. A misinterpretation could lend to harmf ul clinical complications, as shown in the present case.