SUN-319 Incidental Papillary Thyroid Cancer in Primary Hyperparathyroidism: A Case Series

Abstract Disclosure: K. Cadogan: None. S. Narasimhan: None. Background: Incidentally found thyroid nodules in patients with primary hyperparathyroidism (PH) are common. However, it is unclear if there is a relationship between PH and papillary thyroid carcinoma (PTC). This case series explores three cases in which individuals with PH were incidentally found to have PTC to better understand their relationship. Clinical Cases: 46 year old male with hypertension presented with three weeks of myalgias, fatigue, polyuria, and poor oral intake. He was found to have hypercalcemia with PH (Calcium 4.36 mmol/L, n<2.6 mmol/L, PTH 849 pmol/L, n<6.9 pmol/L). Parathyroid scan showed a centrally necrotic parathyroid adenoma (PA) at the right lower pole of the thyroid. CT neck noted a cystic mass on the right thyroid lobe. Right parathyroidectomy and pathology confirmed a parathyroid carcinoma. Post-operatively PTH was 59 pmol/L. Peri-operatively he had hypertension and was managed with Doxazosin and Enalaprilat. Post-operatively he had a fine needle aspiration of the cystic mass which consistent with malignant PTC. Total thyroidectomy seven months later revealed a 0.8 cm tumor in the left thyroid lobe which was identified as PTC. 66 year old female with Lynch syndrome presented with palpitations, dizziness, and back pain. She was hypertensive and started on diuretics. She presented days later with hypertension was found to have hypercalcemia with PH (Calcium 2.98 mmol/L, PTH 116 pmol/L). Parathyroid scan revealed a PA in the left thyroid lobe. Left hemithyroidectomy and pathology confirmed a PA. PTH post-operatively was 47 pmol/L. Three years later surveillance bloodwork showed PH (Calcium 2.93 mmol/L, PTH 269 pmol/L) and parathyroid scan showed a suspected PA in the left thyroid lobe. Total thyroidectomy and pathology confirmed metastatic parathyroid carcinoma and an incidental 0.7 cm PTC in the left middle thyroid. 74 year old female with PH (Calcium 3.49 mmol/L, PTH 586 pmol/L) and Brown tumor. CT identified a suspected PA in the left thyroid. Surgery confirmed hypercellular parathyroid tissue. Post-operative PTH was 49 pmol/L. Surveillance bloodwork post-operatively found PH. Repeat imaging did not show a residual or new adenoma. Exploration of her thyroid four years later lead to a right parathyroidectomy and right hemithyroidectomy. In the resected tissue she was a 2 cm atypical parathyroid tumor suspicious for carcinoma as well as a 1.1 cm cystic PTC. Conclusions: It is unclear if factors such as calcium level or the presence of a malignant parathyroid nodule is associated with incidental PTC in patients with PH. Presentation: Sunday, July 13, 2025