SAT-365 - An Unusual Association: Coexistence of Papillary and Medullary Thyroid Carcinoma in A Patient with Graves' Disease

Background:
The occurrence of papillary thyroid carcinoma (PTC) and medullary thyroid carcinoma (MTC) in the same patient is exceptionally rare. These tumors originate from different cellular lineages and have different behaviors, prognostic factors, and follow-up strategies. Their coexistence is extermerly rare in patients with Graves disease

Case Presentation:
We report a 64-year-old male who was initially evaluated and treated for Graves’ disease complicated by severe Graves’ orbitopathy. He underwent orbital surgical decompression and high-dose corticosteroid therapy followed by orbital radiotherapy, achieving good control of both the orbitopathy. The hyperthyroidism was well controlled with medical management. Thyroid ultrasound revealed a suspicious thyroid nodule requiring fine-needle aspiration. Cytology was reported as Bethesda category V. He underwent total thyroidectomy. Unexpectedly, final histopathological examination demonstrated the coexistence of two distinct thyroid malignancies: papillary thyroid carcinoma and medullary thyroid carcinoma. This dual pathology was confirmed by characteristic histological features and immunohistochemical staining, consistent with their different cellular origins.

Conclusion:
This case represents, to our knowledge, the first reported occurrence of synchronous papillary and medullary thyroid carcinoma in a patient with Graves’ disease. It highlights a rare incidental finding discovered during evaluation for a benign thyroid disorder and underscores the importance of thorough pathological assessment of thyroidectomy specimens. Clinicians should remain aware that more than one malignancy may coexist, even in patients initially managed for non-malignant thyroid conditions. The presence of both tumor types has significant implications for postoperative surveillance, biochemical monitoring, genetic counseling, and long-term management. Reporting such unique cases adds valuable insight to the literature.

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