RESUMO
INTRODUCTION: Graves' disease (GD) is an autoimmune disorder affecting the thyroid gland, leading to systemic manifestations such as hyperthyroidism, Graves' orbitopathy, and pretibial myxedema. Contrary to previous beliefs that hyperthyroidism protects against thyroid cancer, recent studies reveal an increased incidence of thyroid malignancies in GD patients, particularly differentiated thyroid carcinomas and, in rare cases, medullary thyroid carcinoma (MTC). CASE SERIES: This case series presents three female GD patients diagnosed with MTC, highlighting the complexities of diagnosis and management. All patients exhibited thyroid nodules with suspicious ultrasonographic features, elevated plasma calcitonin levels, and required total thyroidectomy. Histological examination confirmed MTC. DISCUSSION: These cases underscore the importance of routine calcitonin screening in GD patients with thyroid nodules to facilitate early detection and improve prognosis. Our findings suggest that while the coexistence of GD and MTC is likely incidental, vigilant monitoring and comprehensive evaluation are crucial for timely intervention. CONCLUSIONS: This study advocates for integrating calcitonin testing into the standard diagnostic protocol for GD patients presenting with thyroid abnormalities.