Evaluation of Diagnostic Accuracy of Medullary Thyroid Carcinoma Using Fine‐Needle Aspiration Cytology—Based on a Single Tertiary Centre Experience

INTRODUCTION: Medullary thyroid carcinoma (MTC) is a rare malignant tumour of the thyroid gland that originates from parafollicular cells. Although rare, MTC is aggressive, so early detection is important for improving prognosis. The accuracy of fine-needle aspiration cytology (FNAC) for diagnosing MTC is still controversial. METHODS: The data of 20 patients who underwent thyroid FNAC with histological follow-up to diagnose MTC between 2016 and 2024 were retrospectively collected from The First Affiliated Hospital of Soochow University. Cytological findings, histological features, and serological testing were reviewed, and causes of misdiagnosis were evaluated. RESULTS: The diagnostic accuracy of FNAC was 90% (18/20). Two patients were initially misdiagnosed with suspected papillary thyroid carcinoma, while eighteen patients were accurately diagnosed in the first instance with suspected MTC. Cytopathological analysis revealed plasmacytoid and spindle-like characteristics with 'salt and pepper' chromatin distributed in the nuclei, with occasional giant tumour cells and frequent deposition of pink-stained amyloid in the background. In addition, serum calcitonin and carcinoembryonic antigen were elevated to varying degrees. CONCLUSION: Fine-needle aspiration is a highly valuable method for the preoperative diagnosis of MTC.