miR-146b measurement in FNA to distinguish papillary thyroid cancer from benign thyroid masses

Thyroid nodules are present in 5–10% of adults on physical palpation of the thyroid gland; it is much higher on thyroid ultrasonography-up to 50–70% in people older than 60 years [1]. One of the main diagnostic problems in the thyroid field involves the preoperative assessment of thyroid nodules. Palpable nodules are common in the adult population, with an estimated prevalence in the United States in the range of 4–7% or 10–18 million affected individuals [2]. Fine-needle aspiration (FNA) is an important method for preoperative evaluation of thyroid nodules, although in 10–20% of samples, the precise diagnosis is unclear, so many are reported as indeterminate or atypical [3]. Most of these patients undergo surgery, although only 8–17% of surgically removed nodules are found to be malignant [2]. Improvement in diagnostic accuracy can be achieved by additional testing of the FNA material for somatic mutations known to occur in thyroid tumours, although its sensitivity is limited because most papillary and follicular cancers have no known mutations [4]. Hence, there is an urgent need for identifying biomarkers that can be used as an adjunct to FNA to distinguish benign thyroid nodules from papillary thyroid cancer (PTC). miRNAs are a class of small noncoding RNAs involved in a wide range of processes such as proliferation, development, apoptosis and metabolism. Microarray miRNAs profile expression analysis in thyroid cancer found aberrant expression of several miRNAs in PTCs. Serum miR124 has value as a diagnostic biomarker in pancreatic cancer, where levels may have prognostic value, and in osteosarcoma, upregulation of miR-21 is associated with poor clinicopathological characteristics [5,6]. In patients with PTC, low miR-199a-3p expression levels are linked to tumour, node and metastases (TNM) stage, extra-thyroidal extension, lymph node metastasis, distant metastasis and recurrence of lymph node metastasis [7]. Several lines of evidence indicate that aberrant miR expression profiles can differentiate thyroid cancers from benign thyroid lesions and normal thyroid tissue, suggesting that miRs may have potential use as a diagnostic tool in thyroid pathology [8,9]. A differential overexpression of miR-146b has been observed in different types of cancer, including PTC [10]. The high expression of miR-146b in PTC has been positively correlated with the malignancy and aggressiveness in clinicopathological correlative studies [11]. In addition, higher miR-146b expression levels had significantly poorer overall survival compared with those with lower miR-146b levels [10]. Up-regulation of tissue miR-146a expression relates to carcinogenesis and deterioration of PTC, so that it may act as potential biomarkers for PTC patients [12]. We hypothesised that miR-146b in FNA can distinguish PTC from benign thyroid masses, and explored possible implications of miR-146b identification on the initial surgical treatment of thyroid nodules with PTC cytology. In addition, we probed links between miR146b expression and key clinicopathological indicators, and so evaluated the potential usefulness of miR-146b in predicting invasion and metastasis in PTC. The Committee on Human Research at the Affiliated Hospital of Qingdao University approved the study. Following informed consent, thyroid tissue samples and clinical and histopathology data were obtained from 336 patients being investigated for suspected thyroid disease at the Department of Thyroid Surgery, Affiliated Hospital of Qingdao University. All patients had FNA before surgery either by direct puncture after palpating the thyroid nodule, or more commonly under ultrasound guidance. Part of the biopsy samples was used for FNA before surgery. Briefly, nodules were aspirated 3 to 5 times with a 22 or 25-gauge needle. From each FNA pass 1–3 smears