Endocrine Abstracts

Introduction: Regardless of the fact that the incidence of thyroid cancer has increased significantly in recent years, the simultaneous occurrence of multiple tumors in one thyroid gland is still a rare phenomenon. These tumors have the morphology, either of a single mass with mixed histological features, or of a single lesion consisting of two distinct cell-populations, or of two different tumors between which normal thyroid tissue is interposed. Various theories have been proposed as causes for the co-existence of papillary and medullary thyroid carcinoma, however the exact mechanism remains unclear.

CASE REPORT: A 42-year-old man referred to our department, for thyroid ultrasound evaluation, that had shown two large nodules in the right lobe (3×2.29 cm, TIRADS-4 and 4.6×2.01 cm, TIRADS-3). Laboratory evaluation showed normal thyroid function, but high calcitonin values 108.9 ng/ml(<14), which raised a strong suspicion of medullary carcinoma. The patient was advised that the best therapeutic approach was surgery, after performing laboratory and imaging tests related to Multiple- Endocrine-Neoplasia-syndromes (MEN). Free 24-hour urinary metanephrines, as well as other indicators of endocrine neoplasms were within normal limits. However, adbominal Computed-Tomography(CT) revealed a mass 2 cm in the left adrenal gland, with increased Hounsfield-units(HU) and absolute-late-washout>50. An additional Magnetic-resonance-imaging(MRI) was deemed necessary, which, due to the SARS-COV-2 pandemic, was not performed immediately. The patient underwent total thyroidectomy, and histology examination revealed mixed thyroid carcinoma with papillary (80%) and medullary (20%) components. Immunohistochemistry was positive for BRAFV600E mutant protein in all neoplastic cells. The patient was treated with ¹³¹I administration, and Whole-Body-Scan(WBS) showed no abnormal findings. Thyroglobulin values with TSH>100 was undetectable, while calcitonin and CEA at 6 and 12 months postoperatively were within normal limits. An abdominal MRI was performed, which did not rule out cystic pheochromocytoma. However, that was not confirmed by the other laboratory and imaging tests(MIBG), nor by clinical symptoms.

Conclusion: Measurement of calcitonin during initial thyroid nodule workup, is helpful in detecting medullary carcinoma. Mixed-medullary-follicular-thyroid-carcinoma(MMFCC) is an extremely rare form of thyroid malignancy and prognostically, the behavior is usually analogous to medullary component. The therapeutic approach is based on the partial treatment of each neoplasm separately. Cystic pheochromocytomas have atypical imaging and clinical features, while symptoms from catecholamine hypersecretion is proportional to the size of the solid part, so these are often silent. In the coexistence of medullary thyroid carcinoma and cystic adrenal lesions, testing for pheochromocytoma is necessary.