LAUSR

Medullary thyroid carcinoma (MTC) is rare, constituting 1–2% of thyroid carcinomas. Calcitonin (Ctn) and carcinoembryonic antigen (CEA) are valuable tumour markers in MTC; Ctn in particular is useful for screening. When there is a suspicion of MTC on cytology, immunohistochemistry of the specimen, Ctn measurement of the aspirate and serum are utilised. Currently there is no international consensus on measuring Ctn levels routinely in patients with thyroid nodules; although it is the standard practice in many European countries, it is considered controversial in the United States of America. A 50-year-old woman presented with a 1.3-cm complex nodule in the left thyroid lobe (Fig. 1A), which was found during a routine examination by her primary physician. There was a history of subclinical hypothyroidism, no family history of thyroid disease or any malignancy. She reported ionising radiation exposure in adulthood only while working as a researcher. The nodule had remained unchanged in appearance and size since its discovery 1.5 years earlier, but she opted for a fine-needle aspiration (FNA). The cytology (Fig. 1B) favoured a cellular adenomatoid nodule; follicular neoplasm was considered a remote possibility. An interval size increase to 1.6 cm observed on a follow-up ultrasound 6 months later prompted a repeat FNA. The smears were less cellular but with morphology similar to the previous fine-needle aspiration cytology (FNAC). However, mildly crowded nuclei and scattered vaguely spindle-shaped cells were noted; the chromatin was fine and homogenous without distinct nucleoli (Fig. 1C,D), suggesting neuroendocrine differentiation. Immunohistochemistry was performed. The tumour cells were positive for AE1/AE3, chromogranin, synaptophysin, thyroid transcription factor 1 (TTF-1) and Ctn, consistent with MTC. Serum Ctn was 1138 pg/mL (normal, 0–5 pg/mL) and CEA was 8.0 ng/mL (normal, 0–2.5 ng/mL). Neck ultrasound was negative for