Medullary thyroid cancers (MTC) account for about 5% of thyroid cancers. The biochemical hallmark of MTC is the secretion of calcitonin (CT). CT levels are both a key feature of pre-operative diagnosis and post-operative follow up. CT screening in a cohort of over 10 000 patients with thyroid nodular disease has demonstrated that a positive CT test has a higher diagnostic sensitivity and specificity for MTC than fine needle aspiration (FNA). They may also secrete carcinoembryonic antigen (CEA). We report a patient with histologically proven MTC with negative CT and CEA pre-operatively who originally presented with evidence of primary hyperparathyroidism.
Case presentation: A 63-year-old retired plasterer attended the endocrinology clinic with biochemical evidence of primary hyperparathyroidism: calcium of 2.76 mmol/l (2.122.60), parathyroid hormone (PTH) level of 76 ng/l (1060), 24 h urinary calcium of 11.2 mmol/24 h (2.57.5), vitamin D replete. Pre-operative investigation revealed a 2.5×1.7×1.4 cm dominant left thyroid nodule which was hypoechoic and associated with specks of calcification. FNA was reported as THY3, consistent with a follicular neoplasm. Owing to the association of MTC with primary hyperparathyroidism in MEN2 he had a pre-operative assessment of CT and CEA. CT was reported on 2 separate occasions as <11 ng/l (<11) and 12 ng/l (<11). CEA was 4.1 μg/l (<5). Overnight urinary metanephrine and normetanephrine levels as well as plasma metanephrines and normetanephrines assessed pre-operatively were normal.
The patient underwent bilateral neck exploration with left hemi-thyroidectomy. The overall histological features were consistent with medullary thyroid carcinoma pT1b pNX pMX (TNM 7th edition). Immunohistochemistry showed diffuse cytoplasmic positivity for CT and heterogeneous labelling with CEA. His RET proto oncogene status is awaited. These patients may constitute a subset of patients with atypical MTC where the tumour can produce CT (hence positive staining) but is unable to secrete the protein.