Ultrarapid <i>BRAF</i> mutation detection on supernatant cell‐free DNA obtained by FNA: An accurate and expedient method for <i>BRAF</i> assessment in aggressive thyroid carcinomas

BACKGROUND: For patients with aggressive thyroid cancer, including anaplastic thyroid carcinoma (ATC) and high-grade follicular cell-derived non-anaplastic thyroid carcinoma, rapid BRAF p.V600E testing is critical as targeted therapy with BRAF/MEK inhibitors significantly improves outcomes. This study assesses the performance and turnaround time (TAT) of the Biocartis Idylla platform for ultrarapid BRAF p.V600E detection across various preparations, emphasizing the use of residual CytoLyt material (supernatant cell-free DNA [ScfDNA]). METHODS: All histologically confirmed cases of aggressive thyroid carcinomas received for Idylla testing were identified. Samples were prepared either as ScfDNA, formalin-fixed paraffin-embedded (FFPE) cell block (CB), Diff-Quik smear, or surgical FFPE samples. BRAF p.V600E testing was performed on the Idylla platform, and results were compared to a clinically validated reference method of either next-generation sequencing (NGS) or digital-droplet polymerase chain reaction (ddPCR). TAT for Idylla testing on ScfDNA samples was compared to FFPE preparations and to BRAF V600E immunocytochemistry (ICC). RESULTS: Fifty-seven samples (including 51 ATC) were tested by Idylla. The overall success rate for Idylla was 91%, with ScfDNA at 90% and surgical FFPE specimens at 100%. Of 42 samples that had NGS/ddPCR testing, concordance with the reference method showed 100% agreement (excluding failures) across all sample types. TAT for Idylla on ScfDNA samples was significantly shorter than ICC (median 2.86 vs. 46.7 hrs, p < .05). CONCLUSION: The Idylla BRAF assay delivers ultrarapid results that are both reliable and accurate with high success rates, particularly on ScfDNA samples. ScfDNA samples also have the fastest TAT because no histologic processing or pre-extraction are required for testing.