Paraganglioma-like medullary thyroid carcinoma: a rare entity.

OBJECTIVE

The wide variety of rare histologic variants of medullary thyroid carcinoma (MTC) may make the differential diagnosis difficult. Pathologic examination of the resected specimen will not always be able to confirm the diagnosis, leaving the surgeon with an uncertainty as to what type of resection is best for the patient. The following report describes the case of a 58-year-old man with the rare diagnosis of paraganglioma-like MTC.

METHODS

The patient presented with markedly elevated calcitonin (CT) and carcinoembryonic antigen (CEA) levels. A 1-cm tumor was detected in the right lobe of the thyroid. Based on the clinical diagnosis of MTC, we performed a total thyroidectomy with lymphadenectomy of the central and right lateral compartments. Paraffin sections of the resected specimen were stained with hematoxylin and eosin (H&E) and immunohistochemically characterized using antibodies to CT, CEA, chromogranin A, thyroglobulin, synaptophysin, sustentacular cells (SCs), low- and high-molecular cytokeratins (CK 5/6, 7, 18, 20), epidermal growth factor-receptor (EGFR), thyroid transcription factor-1 (TTF-1), bcl-2, Melan A, C-kit, neuron-specific enolase (NSE), and galectin-3. The patient's blood and tumor tissue were examined for mutations in the RET-protooncogene.

RESULTS

H&E staining of both frozen and permanent sections was unable to differentiate benign from malignant tissue. Typical morphologic characteristics for MTC were completely absent. Only the additional finding of positivity for synaptophysin and numerous SC cells visible in-between neoplastic cells made the diagnosis of paraganglioma-like MTC possible. Sequencing of the RET proto-oncogene revealed no mutations.

CONCLUSIONS

There are subgroups of MTC that present clinically similar to classic MTC, but in which missing typical morphologic characteristics make histopathology diagnosis difficult. In these cases, diagnosis, operative decisions, and follow-up strategies should be based on preoperative biochemical markers, imaging findings, and clinical parameters in accordance to the guidelines for classic MTC.