Molecular Testing for and Mutations from Cytoscrapes of Thyroid Fine Needle Aspirates: A Single-Center Pilot Study

Context And Aim: Molecular testing of thyroid FNA has been advocated in the indeterminate categories of The Bethesda System for Reporting Thyroid Cytopathology (TBSRTC) 2018. The utility of cytoscrapes of thyroid FNA samples for V600E and mutations was evaluated in this pilot study.

Methods And Materials: Thyroid FNA samples between 2015 and 2018 from TBSRTC categories 3-6 were included. DNA was extracted from one to two representative smears (cytoscrape). Real-time PCR for V600E and (, , and ) gene mutations was performed. Histopathology correlation was available in 44 cases.

Statistical Methods: Chi-square test and calculation of sensitivity, specificity, and positive/negative predictive values were performed.

Results: A total of 73 thyroid FNA cases and 11 nodal metastases of papillary thyroid carcinoma (PTC) were evaluated. The DNA yield ranged from 1.9 to 666 ng/μl (mean 128 ng/μl) in 80 cases and was insufficient in four cases. Overall, mutations were seen in 45 (56.25%) cases with V600E, , , and in 21 (46.7%), 19 (42.2%), 4, and 1 cases, respectively. V600E mutation was seen in PTC (11/18, 61%), nodal PTC metastases (5/10, 50%), and occasionally in TBSRTC category 3 (1/18, 5.5%). mutations were seen across all categories and were maximum in the AUS/FLUS group (6/18, 33%). V600E /RAS testing had an overall sensitivity, specificity, and positive and negative predictive values of 61.7%, 80%, 91.3%, and 38%, respectively, for the detection of malignancy. In indeterminate thyroid nodules, the sensitivity, specificity, PPV, and NPV were 56.2%, 80%, 81.8%, and 53.3%, respectively.

Conclusion: V600E/RAS mutation testing from cytoscrapes are useful as a rule-in test for indeterminate thyroid nodules and provide molecular confirmation in nodal metastases of PTC.