alexa Assessment of cellularity, genomic DNA yields, and technical platforms for BRAF mutational testing in thyroid fine-needle aspirate samples.
Molecular Biology

Molecular Biology

Journal of Cytology & Histology

Author(s): Dyhdalo K, Macnamara S, Brainard J, Underwood D, Tubbs R,

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Abstract BACKGROUND: BRAF mutation V600E (substitution Val600Glu) is a molecular signature for papillary thyroid carcinoma (PTC). Testing for BRAF mutation is clinically useful in providing prognostic prediction and facilitating accurate diagnosis of PTC in thyroid fine-needle aspirate (FNA) samples. METHODS: This study assessed the correlation of cellularity with DNA yield and compared 2 technical platforms with different sensitivities in detection of BRAF mutation in cytologic specimens. Cellularity was evaluated based on groups of 10+ cells on a ThinPrep slide: 1+ (1-5 groups), 2+ (6-10 groups), 3+ (11-20 groups), and 4+ (> 20 groups). Genomic DNA was extracted from residual materials of thyroid FNAs after cytologic diagnosis. RESULTS: Approximately 49\% of thyroid FNA samples had low cellularity (1-2+). DNA yield is proportionate with increased cellularity and increased nearly 4-fold from 1+ to 4+ cellularity in cytologic samples. When applied to BRAF mutational assay, using a cutoff of 6 groups of follicular cells with 10+ cells per group, 96.7\% of cases yielded enough DNA for at least one testing for BRAF mutation. Five specimens (11.6\%) with lower cellularity did not yield sufficient DNA for duplicate testing. Comparison of Sanger sequencing to allele-specific polymerase chain reaction methods shows the latter confers better sensitivity in detection of BRAF mutation, especially in limited cytologic specimens with a lower percentage of malignant cells. CONCLUSIONS: This study demonstrates that by using 6 groups of 10+ follicular cells as a cutoff, nearly 97\% of thyroid FNA samples contain enough DNA for BRAF mutational assay. Careful selection of a molecular testing system with high sensitivity facilitates the successful conduction of molecular testing in limited cytologic specimens. Cancer (Cancer Cytopathol) 2014;122:114-22 © 2013 American Cancer Society. © 2013 American Cancer Society. This article was published in Cancer Cytopathol and referenced in Journal of Cytology & Histology

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