[BRAF V600E mutation in papillary thyroid carcinoma: prevalence and detection in fine needle aspiration specimens]

Highly Sensitive Detection of Low-Abundance BRAF V600E Mutation in Fine-Needle Aspiration Samples by Zip Recombinase Polymerase Amplification

Papillary thyroid carcinoma (PTC) is the most common thyroid cancer with high incidence in endocrine tumors, which emphasizes the significance of accurate diagnostics. Still, the commonly used cytological method (fine-needle aspiration (FNA) cytology) and molecular diagnostic methods (such as PCR and sequencing) are limited in terms of diagnostic time, sensitivity, and user-friendliness. In this study, we introduce a novel Zip recombinase polymerase amplification (Z-RPA) strategy to efficiently detect rare mutant alleles in PTC fine-needle aspiration samples, which is sensitive, fast, and simple to manipulate. Using Zip nucleic acid (ZNA) probes to clamp the mutation region, the phi 29 polymerase could selectively displace mismatched ZNA probes and start amplification, while leaving complementary ZNA probes untouched and blocking amplification according to genotype. We demonstrated the good sensitivity and specificity of this strategy with optimized conditions and design, which enabled detection of BRAF V600E mutation in a total 4 ng of genomic DNA within 40 min (≈1 copy). Robust behavior in clinical specimen analysis was also demonstrated. The Z-RPA strategy provides a pragmatic approach to rapidly, sensitively, and easily detect BRAF V600E mutation in clinical fine-needle aspiration samples, which is a promising method for early cancer diagnosis and treatment guideline.

Molecular Variants and Their Risks for Malignancy in Cytologically Indeterminate Thyroid Nodules

Background: Gene panels are routinely used to assess predisposition to hereditary cancers by simultaneously testing multiple susceptibility genes and/or variants. More recently, genetic panels have been implemented as part of solid tumor malignancy testing assessing somatic alterations. One example is targeted variant panels for thyroid nodules that are not conclusively malignant or benign upon fine-needle aspiration (FNA). We systematically reviewed published studies from 2009 to 2018 that contained genetic data from preoperative FNA specimens on cytologically indeterminate thyroid nodules (ITNs) that subsequently underwent surgical resection. Pooled prevalence estimates per gene and variant, along with their respective positive predictive values (PPVs) for malignancy, were calculated. Summary: Our systematic search identified 540 studies that were supplemented by 18 studies from bibliographies or personal files. Sixty-one studies met all inclusion criteria and included >4600 ITNs. Overall, 26% of nodules contained at least 1 variant or fusion. However, half of them did not include details on the specific gene, variant, and/or complete fusion pair reported for inclusion toward PPV calculations. The PPVs of genomic alterations reported at least 10 times were limited to BRAF^V600E (98%, 95% confidence interval [CI 96-99%]), PAX8/PPARG (55% [CI 34-78%]), HRAS^Q61R (45% [CI 22-72%]), BRAF^K601E (42% [CI 19-68%]), and NRAS^Q61R (38% [CI 23-55%]). Excluding BRAF^V600E, the pooled PPV for all other specified variants and fusions was 47%. Multiple variants within the same nodule were identified in ∼1% of ITN and carried a cumulative PPV of 77%. Conclusions: The chance that a genomic alteration predicts malignancy depends on the individual variant or fusion detected. Only five alterations were reported at least 10 times; BRAF^V600E had a PPV of 98%, while the remaining four had individual PPVs ranging from 38% to 55%. The small sample size of most variants and fusion pairs found among ITNs, however, limits confidence in their individual PPV point estimates. Better specific reporting of genomic alterations with cytological category, histological subtype, and cancer staging would facilitate better understanding of cancer prediction, and the independent contribution of the genomic profile to prognosis.

Contribution of the BRAF oncogene in the pre-operative phase of thyroid carcinoma

Numerous experiments have been conducted over the last few years aiming to identify molecular markers that show the diagnostic accuracy of fine-needle aspiration (FNA), particularly in thyroid lesions that are considered indeterminate. Using certain search arguments and previously defined criteria, 37 studies reporting experiments with the BRAF mutation in pre-operative FNA of the thyroid were selected from the electronic databases PUBMED, MEDLINE, SCOPUS and LILACS, in order to gather evidence with regard to the possible contribution of BRAF in the management of thyroid carcinoma. There were no cases positive for BRAF in follicular carcinomas (FTCs), Hürthle cell carcinomas (HCCs) or medullary thyroid carcinomas (MTCs). Among the 11 cases of anaplastic thyroid carcinomas (ATC), three showed positive results for the BRAF mutation. The number of cases positive for BRAF among the benign lesions was not significant. The average prevalence of BRAF-positive cases in papillary carcinomas (PTC) was 58.6%, while in follicular variants of papillary carcinoma (FVPTC), the average prevalence was 29.6%. For lesions diagnosed as indeterminate or suspicious, the average prevalence of BRAF positivity in PTC was 48.5%. The experiments included in the present study indicated a specificity of almost 100% and a high predominance of the BRAF mutation in PTC, distinguishing the marker in the planning and medical management of papillary carcinoma of the thyroid.

Immunocytochemistry with cytokeratin 19 and anti-human mesothelial cell antibody (HBME1) increases the diagnostic accuracy of thyroid fine-needle aspirations: preliminary report of 150 liquid-based fine-needle aspirations with histological control

BACKGROUND

Thyroid nodules are relatively common (7% of the population) but are malignant in only 5%-10% of cases. Fine-needle aspiration (FNA) to detect cancer can have > 90% sensitivity but only 50%-65% specificity because of false-positive results, which necessitates surgical controls. We aimed to assess the diagnostic accuracy of immunocytochemistry (ICC) of thyroid FNA to improve its sensitivity and specificity.

METHODS

We prospectively collected 2038 thyroid FNAs, of which 1397 were FNA biopsies with liquid-based cytology (Thin-Prep-Hologic®). ICC with cytokeratin 19 and HBME1 antibodies (Dako® A/S) was used for all malignant cases and cases of atypical cells of undetermined significance (AUS), follicular neoplasm (FN), and nodules suspicious for malignancy-papillary thyroid carcinoma (SM-PTC) as well as some benign cases (abnormal features on radiography or benign on secondary FNA). ICC results were defined as "non-contributory," "favoring benign," "favoring malignant," or "indeterminate." Results for 150 cases were compared with histological controls for diagnostic accuracy.

RESULTS

Of these 150 cases ICC was helpful for benign or malignant triage of 48 cases of AUS, FN, and SM-PTC (42% of these lesions). Six (4%) ICC results were false positive (favoring malignant with benign histology) but none were false negative (favoring benign with malignant histology). Results for indeterminate cytological cases favored malignant or benign disease with sensitivity, specificity, and negative and positive predictive values of 100%, 85.2%, 100%, and 86.2%, respectively.

CONCLUSIONS

ICC of thyroid FNAs with cytokeratin 19 and HBME1 antibodies can reduce the false-positive and false-negative results of single morphological analyses. It can increase the sensitivity and specificity of diagnosis, thus improving diagnostic accuracy and reducing the need for surgical controls.