An effective approach for BRAF V600E mutation analysis of routine thyroid fine needle aspirates.

INTRODUCTION: Molecular testing for genetic alterations in thyroid neoplasms, including BRAF V600E (BRAF) mutation, are often applied to thyroid aspirates falling into the Bethesda System for Reporting Thyroid Cytopathology indeterminate categories. Current methods typically use dedicated aspirated material, without morphological determination of containing the cells of interest and may be of elevated cost. We describe our experience with BRAF mutation analysis on material obtained from Papanicolaou (PAP)-stained ThinPrep® (TP) slides. METHODS: Eighty-three cases collected between 2012 and 2019 with more than 100 cells were selected. An electronic record of a whole slide scan was made for each case before testing. The coverslips were removed, and DNA was extracted from material scraped from each slide using the Qiagen QIAamp DNA FFPE Tissue Kit. BRAF testing was performed using a highly sensitive mutation detection assay, either COLD-PCR, castPCR, or droplet digital PCR. RESULTS: Fourteen out of 83 cases had a BRAF mutation. Of these, 8 were classified as atypia of undetermined significance or suspicious for malignancy in which follow-up showed conventional papillary thyroid carcinoma in 5 out of 6 cases. The specificity and positive predictive value were 97% and 91%, respectively. CONCLUSIONS: BRAF mutation analysis can be performed on material obtained from routine clinical PAP-stained TP slides. As a first step, this unconventional effective approach may reduce costs related to the molecular evaluation of thyroid nodule aspirates and provides the opportunity for cytomorphological confirmation that the cells of interest are present in material submitted for BRAF mutation analysis.