Introduction

Molecular testing for genetic alterations in thyroid neoplasms, including BRAF V600E (BRAF) mutation, are often applied to thyroid aspirates that fall into the Bethesda System for reporting thyroid cytology indeterminate categories. Current methods typically use dedicated aspirated material, without morphologic determination if this material contains 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 2012-2019 with more than 100 cells were selected. An electronic record of a whole slide scan was made for each case before BRAF 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 with 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 cytomorphologic confirmation that the cells of interest are present in the material submitted for BRAF mutation analysis.