Core-needle biopsy for the preoperative diagnosis of follicular neoplasm in thyroid nodule screening: A validation study

The role of ultrasound-guided core-needle biopsy (CNB) for the diagnosis of follicular neoplasm (FN) in the screening of thyroid nodules is controversial. We developed a diagnostic system for FN in CNB specimens and aimed to validate the clinical usefulness of the method compared with fine-needle aspiration cytology (FNAC). We reviewed 5993 FNACs and 1303 CNBs from the pathology database at Seoul St. Mary's Hospital between August 2012 and December 2014. The diagnostic rate of FN was significantly higher in CNB than in FNAC (15.7% vs. 2.4%, respectively; P<0.001). A total of 289 cases (117 FNACs and 172 CNBs) were confirmed histologically after surgical resection. NRAS mutation testing was performed with pyrosequencing. Comparing the FNAC and CNB groups, there were no differences in the positive predictive values for neoplasm (84.6% vs. 89.0%, respectively; P=0.200) and malignancy (48.7% vs. 43.0%, respectively; P=0.340). When we excluded the noninvasive encapsulated follicular variant of papillary carcinoma from the malignancy group, there was also no significant difference in the malignancy risk between the two groups (22.7% and 27.4% in the CNB and FNAC groups, respectively; P=0.365). The NRAS mutation rate was 26.5% (57/215) in all FNs and occurred with similar frequency in both groups. The sensitivity, specificity, positive predictive value, and negative predictive value of a NRAS testing to predict malignancy were 40.6%, 84.9%, 68.4%, and 63.9%. In conclusion, FN was more frequently diagnosed in the CNB group than in the FNAC group, but the rates of malignancy, neoplasm, and NRAS mutation were equivalent in both groups. Therefore, CNB is a good method for the diagnosis of FN in thyroid nodule screening.