Fine-needle aspiration of metastatic papillary thyroid carcinoma found in the liver

Papillary thyroid carcinoma (PTC) metastasis to the liver is a rare event and may cause diagnostic dilemmas. In this study, we have reviewed the cytological features of metastatic PTC to the liver, tested the BRAF V600E status of these lesions, and discussed potential diagnostic pitfalls. The pathological archives at the Johns Hopkins Hospital were searched for metastatic PTC. A total of 247 cases were identified; four cases were found to have metastases to the liver. Three of these cases were available for molecular testing to determine BRAF V600E status. All patients were female with ages ranging from 39- to 66-years old. Local lymph node involvement was found in all patients at the time of thyroidectomy. The average time of liver metastasis discovery following thyroidectomy was 16 years. The cytomorphology revealed predominantly microacini or two-dimensional clusters. Tumor cells were small-to-intermediate in size with oval nuclei, fine chromatin, nuclear grooves, rare intranuclear pseudoinclusions, and mitoses. In all cases, immunohistochemical stains for thyroglobulin and thyroid transcription factor 1 (TTF-1) were positive. All these tested cases were negative for the BRAF V600E mutation. The differential diagnosis includes adenocarcinoma and neuroendocrine neoplasms. The most important morphologic features for diagnosing PTC are the presence of pale finely granular chromatin, nuclear grooves, and intranuclear pseudoinclusions. A thorough review of the patient's clinical history and the use of appropriate IHC stains are essential in reaching an accurate diagnosis. Further molecular characterization is necessary to identify the changes most strongly associated with distant metastasis.