Endocrine Abstracts

JOINT181

Background: The rare coexistence of medullary thyroid carcinoma (MTC) and papillary thyroid carcinoma (PTC) in Multiple Endocrine Neoplasia type 2A (MEN2A) presents unique challenges in diagnosis and treatment.

Case Presentation: We report a 28-year-old Chinese female diagnosed with MEN2A, initially presenting with multifocal MTC on fine needle aspiration of right thyroid nodules. The patient underwent total thyroidectomy, tracheoesophageal groove clearance, and right neck dissection. Histopathological examination of the thyroidectomy specimen revealed dual pathology: multifocal MTC in both lobes and unifocal PTC at the isthmus. Regional lymph node involvement was significant, with most showing metastatic MTC, and three level 6 lymph nodes exhibiting metastatic PTC.

Discussion: MEN2A is an autosomal dominant hereditary syndrome characterized by MTC, pheochromocytoma, and primary hyperparathyroidism, resulting from germline mutations in the RET proto-oncogene. These mutations lead to tumorigenesis through gain-of-function alterations. Although MTC is nearly universal in MEN2A and typically multifocal and bilateral, the coexistence of MTC and PTC in the same thyroid gland is extremely rare. Such cases may present as a mixed tumor with dual differentiation or as a collision tumor. Recent studies suggest that RET point mutations may also induce oncogenic activity in thyroid follicular cells, potentially contributing to PTC development. Distinguishing between MTC and PTC is crucial for management as treatment strategies differ significantly. While the American Thyroid Association (ATA) guidelines recommend TSH suppression to reduce recurrence risk in PTC, this is ineffective for MTC due to the absence of TSH receptors on thyroid C cells. Consequently, patients with dual pathology require a tailored therapeutic strategy to optimize the management of both malignancies.

Conclusion: The coexistence of MTC and PTC in MEN2A underscores the need for comprehensive histopathological evaluation and genetic analysis to guide appropriate clinical management.