Detection of BRAF Mutations on Direct Smears of Thyroid Fine Needle Aspirates Using the Cell Transfer Technique

Abstract

Introduction: A mutation of the BRAF gene is the most common genetic alteration in papillary thyroid carcinoma (PTC). Molecular techniques that can identify BRAF mutations could be an important ancillary tool in the diagnosis of thyroid carcinoma, especially in cases of indeterminate thyroid fine needle aspirates (FNA). The cell transfer technique (CTT) has proven to be useful for obtaining cells for molecular testing from FNA direct smears. Materials and Methods: PCR-based BRAF molecular testing was performed on one air-dried and one ethanol-fixed CTT smear prepared from a thyroid FNA and on sections obtained from the corresponding thyroidectomy formalin-fixation paraffin embedded (FFPE) blocks from 31 cases diagnosed by histopathologic assessment as classical PTC (18), follicular variant PTC (4), follicular carcinoma (1), follicular adenoma (1) and benign non-neoplastic lesions (7). Results: BRAF testing was successfully performed on 30/31 air-dried CTT (97%), 28/31 ethanol-fixed CTT (90%) and 28/31 FFPE (90%). The results included 12 BRAF mutations and 18 wild types (WT) for the air-dried CTT, 14 BRAF mutations and 14 WT for the ethanol-fixed CTT and 13 BRAF mutations and 15 WT for the FFPE. The concordance rate between air-dried and ethanol-fixed CTT was 96% and was 86% between CTT and FFPE. There were 2 mutations detected on CTT which were WT on the corresponding FFPE. Conversely, 2 mutations identified on the FFPE were WT on the corresponding CTT. Conclusions: Using the FFPE as the gold standard, the sensitivity and specificity for detection of BRAF mutation on the CTT direct smears were 85% and 87%, respectively. BRAF mutation is a highly specific marker for thyroid carcinoma. For those patients with indeterminate thyroid FNA results, the use of CTT to select atypical cells for the BRAF mutation analysis should enhance the diagnostic sensitivity for thyroid FNA and reduce the need for repeat aspirates.