Molecular and clinical features of papillary thyroid cancer in adult patients with a non-classical phenotype

Unveiling the BRAF fusion structure variations through DNA and RNA sequencing

BACKGROUND

The detection of BRAF fusions by using next-generation sequencing (NGS) is essential for comprehensive analysis.

METHODS

Data BRAF positive rearrangements from Chinese cancer patients were analyzed. DNA NGS was performed on FFPE samples, and RNA NGS was used to confirm fusion transcripts.

RESULTS

BRAF fusions were identified in various cancers, predominantly glioma (87.8%). DNA NGS detected 371 BRAF fusion-positive samples, with 338 retaining the serine/threonine receptor tyrosine kinase domain (RTKD), divided into four groups: common (n = 254), rare (n = 66), intergenic (n = 7), and exonic (n = 11) fusions. Common fusions, mainly KIAA1549-BRAF, comprised the majority, with variations at introns 8, 9, and 10. Rare fusions and intergenic/exonic breakpoints displayed diverse structural patterns. RNA NGS verified transcriptional consistency in most samples from common fusions. However, various outcomes at the RNA level were found in other groups, involving mechanisms like alternative splicing, antisense rearrangement, and frameshift rearrangement. Additionally, 33 fusions lacked the RTKD, demonstrating significant structural diversity. Furthermore, 22 novel fusions were identified, which were distributed in tongue cancer, liver cancer, lung cancer, melanoma, brain cancer, and colon cancer.

CONCLUSIONS

Comprehensive molecular profiling and RNA sequencing are essential for accurate fusion detection, improving the design of NGS panels and aiding in the targeted therapy of BRAF fusion-positive cancers.

Diagnostic utility of RAS mutation testing for refining cytologically indeterminate thyroid nodules

RAS mutations are prevalent in indeterminate thyroid nodules, but their association with malignancy risk and utility for diagnosis remains unclear. We performed a systematic review and meta-analysis to establish the clinical value of RAS mutation testing for cytologically indeterminate thyroid nodules. PubMed and Embase were systematically searched for relevant studies. Thirty studies comprising 13,328 nodules met the inclusion criteria. Random effects meta-analysis synthesized pooled estimates of RAS mutation rates, risk of malignancy with RAS positivity, and histologic subtype outcomes. The pooled mutation rate was 31 % (95 % CI 19-44 %) among 5,307 indeterminate nodules. NRAS mutations predominated at 67 % compared to HRAS (24 %) and KRAS (12 %). The malignancy rate with RAS mutations was 58 % (95 %CI=48-68 %). RAS positivity increased malignancy risk 1.7-fold (RR 1.68, 95 %CI=1.21-2.34, p=0.002), with significant between-study heterogeneity (I2=89 %). Excluding one outlier study increased the relative risk to 1.75 (95 %CI=1.54-1.98) and I2 to 14 %. Funnel plot asymmetry and Egger's test (p=0.03) indicated potential publication bias. Among RAS-positive malignant nodules, 38.6 % were follicular variant papillary carcinoma, 34.1 % classical variant, and 23.2 % follicular carcinoma. No statistically significant difference in the odds of harboring RAS mutation was found between subtypes. In conclusion, RAS mutation testing demonstrates clinical utility for refining the diagnosis of cytologically indeterminate thyroid nodules. Positivity confers a 1.7-fold increased malignancy risk, supporting use for personalized decision-making regarding surgery vs. monitoring. Follicular variant papillary carcinoma constitutes the most common RAS-positive malignant histological subtype. See also the graphical abstract(Fig. 1).