Structure of the BRAF protein.
The application of molecular markers is already significantly improving the diagnosis of thyroid cancer, according to several studies presented during the 82nd annual meeting of the American Thyroid Association, and broader application of mutational panels to tumor samples could help prevent unnecessary surgeries to confirm the diagnosis.
Lindsey Kelly, MD, and colleagues at the University of Pittsburgh Medical Center analyzed 501 papillary carcinomas from 480 patients for commonly tested as well as for rare mutations. Point mutations, including BRAF exon 15
, as well as BRAF
rearrangement, were detected by real-time polymerase chain reaction (RT-PCR) testing and fluorescent melting cure analysis and Sanger sequencing. Rearrangements of PAX8/PPARgamma
, and RET/PTC3
were detected by TaqMan RT-PCR assays.
“Of 501 tumors, 456 had sufficient material available for informative molecular testing,” investigators noted. Of these, 69.5% of the samples tested were found to be positive for commonly tested mutations including 184 BRAFV600E
, found in approximately 40% of the samples, followed by NRAS61
, found in 18% of the samples and HRAS
in approximately 7%. Much lower levels of other commonly tested mutations including RET/PTCI, RET/PPTC3
, and PAX8/PPARgamma
were also detected.
In addition, investigators identified rare mutations in 3.7% of the samples. Rare mutations in the papillary carcinomas tested included KRAS61
, and NTRK1
rearrangements. They also identified 2 rare RET
rearrangements and 3 rare BRAF
rearrangements or point mutations.
Conversely, approximately 27% of the tumor samples tested were negative for mutations. The investigators pointed out that the majority of these were the follicular variant of papillary thyroid cancer.
“Our analysis of a large series of papillary carcinomas reveals that common mutations are found in 69.5% of tumors, whereas additional known point mutations and rearrangements can be detected in 3.7% of tumors,” investigators observed. “These mutations, with KRAS codon 61
mutation and NTRK1
rearrangements [being the] most prevalent, should be added to the routine mutational panel to improve detection of papillary carcinoma in thyroid fine-needle aspiration (FNA) samples.”
Meanwhile, in a separate study, Markus Eszlinger, PhD, of University of Leipzig in Germany and colleagues demonstrated that detection of rearrangements (PAX8/PPARgamma, RET/PTC
) as well as point mutations BRAF, NRAS, HRAS,
is feasible using air-dried fine-needle aspirations. As he reported during the same meeting, researchers extracted RNA and DNA from 310 routine air-dried FNA smears, 164 of which were indeterminate, 57 of which were malignant, and 89 of which were non-neoplastic.
They also examined corresponding formalin-fixed paraffin-embedded tissue samples of 156 follicular ademonas, 32 follicular thyroid carcinomas, 9 follicular variant papillary thyroid carcinomas, 44 papillary thyroid carcinomas, and 69 goiters. Using various sequencing techniques, they found that molecular screening of these FNA samples increased the sensitivity from 67% for cytology alone to 75% in the total set. In the indeterminate set with 19 follicular thyroid cancers, the sensitivity of detecting carcinomas and mutation-positive adenomas was 48%, and the specificity was 99%. As investigators pointed out, genetic sequencing for rearrangements and point mutations has been emerging as a nonsurgical approach to the diagnosis of thyroid cancer.
Until now, however, genetic aberrations have only been detected in fresh FNA samples. Screening of air-dried FNA samples with a panel of genetic mutations linked to follicular and papillary thyroid cancer could reduce the need for diagnostic surgery, as investigators suggested.
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