The poor prognosis associated with ATC is primarily attributed to the limited efficacy of conventional treatment modalities and an incomplete understanding of the underlying mechanisms driving ATC tumorigenesis. This study aimed to address these challenges by conducting comprehensive genomic profiling of 26 ATC cases in Taiwan and assessing the concordance between tissue and liquid NGS in 13 ATC cases. The genomic landscape of ATC revealed the intricate involvement of multiple pathways, including RAS/RAF/MEK/ERK (73.1%), PI3K/AKT/mTOR (57.7%), cell cycle regulation (92.3%), other receptor tyrosine kinases (65.4%), DNA damage response (50.0%), DNA mismatch repair (34.6%), and chromatin remodeling (76.9%). Liquid NGS demonstrated the capability to detect more BRAF mutations in cases where tissue was either unavailable or insufficient13. These findings underscore the highly heterogeneous genetic background of ATC, revealing previously unexplored genetic events. Notably, mutations in HER1/2/3, FGFR2/4, NTRK 1/2/3, and genes associated with the DNA damage response have been identified, presenting intriguing possibilities, as pharmaceuticals targeting these genes are currently in clinical or experimental use. Finally, the mutation landscape of the cohort was characterized, revealing diverse frequencies of recognized thyroid malignancy genes in the majority, though not all, of ATC cases.
The detection of driver mutations is a key factor in ATC treatment, as most patients cannot be cured by surgery alone. The commonly mutated genes were TP53 in 17/26 (65.4%) patients, and BRAF in 8/26 (30.8%) patients, which is consistent with previous reports14–17. In addition to tumor agnostic therapy, combination therapy with dabrafenib and trametinib is the only targeted therapy that has been approved for ATC harboring the BRAF V600E mutation since 2018, based on the ROAR study (BRF117019 study, NCT02034110)11,18. A few retrospective studies also confirmed the role of targeted therapy for BRAF-mutated ATC19,20. Tumor agnostic treatment was applied for ATC with NTRK fusion, RET fusion, MSI-H, and TMB-H, which were not found in the current cohort. However, other possible novel targets have been identified, providing evidence for the development of targeted therapies.
Regarding KRAS mutations, we identified one G12V, one Q61H, and one Q61K mutation. Sotorasib and adagrasib have been approved for patients with non-small cell lung cancer (NSCLC) harboring the KRAS G12C21. In 14 patients (10 with pancreatic ductal adenocarcinoma (PDAC) and four with NSCLC) harboring G12X mutations other than G12C and treated with RMC-6236 at least 8 weeks before the data cut-off date, the objective response rate was 36%22. Ongoing investigations into targeted therapies offer hope for the treatment of cancers with various KRAS mutations21.
Four patients with NRAS mutations were identified, including four with Q61R and one with G13R mutations. Currently, there is no approved treatment for cancers with NRAS mutations. However, MEK inhibitors such as cobimetinib, trametinib, and binimetinib may stabilize NRAS-mutated metastatic melanoma, with an objective response rate (ORR) of 18.2% and a disease control rate (DCR) of 48.5%23. Recently, the ORR reported was 46.7% in patients with NRAS-mutated melanoma treated with naporafenib (a pan-RAF kinase inhibitor, 200 mg twice a day) plus trametinib (1 mg once daily)24. SEACRAFT-1 is an open-label study designed to assess the safety and efficacy of naporafenib administered with trametinib in previously treated patients with locally advanced unresectable or metastatic RAS Q61X solid tumor malignancies including thyroid cancer (ClinicalTrials.gov Identifier: NCT05907304).
Other genetic alterations involving the DNA damage response (DDR) and cell cycle may have implications in specific targeted therapies. Currently, homologous recombination deficiency (HRD) is the only available predictive biomarker that can identify patients more likely to benefit from PARP inhibitors25. PARP inhibitor monotherapy has been extensively investigated in cancer subtypes commonly associated with HRD26. Furthermore, clinical trials of combination strategies with anti-angiogenesis and immunotherapy have aimed to enhance the efficacy of PARP inhibitors26. Studies targeting cell cycle checkpoints27, such as ATM28, ATR, and Wee129, are ongoing to tackle the DDR.
In our study, the rate of BRAFV600E detection by circulating tumor DNA (ctDNA) was 26.7%. This is comparable to the findings in 92 cases of ATC using the Guardant360 plasma NGS test, which showed a BRAFV600E detection rate of 27.2%30. However, this was lower than that reported in historical cohorts14–17 and in our tissue NGS (30.8%).
In the current cohort of 13 NGS pairs, the concordance rates were 84.6% for BRAF and 69.2% for TP53. This discrepancy in detection rates could potentially be attributed to the specific characteristics of ATC, including tumor burden and shedding. Supporting this, another study involving 23 patients with ATC at the University of Texas MD Anderson Cancer Center revealed that the reliability of inference based on concordance was highest in patients who underwent dual-platform sequencing before initiating definitive treatment17. In contrast, it was the lowest in patients who underwent cell-free circulating DNA (cfDNA) analysis after treatment17. Therefore, tissue NGS should remain the standard of care for determining therapeutic options for ATC unless the tissue is unavailable or insufficient for tissue NGS.
The identification of more novel targets and resistance mechanisms is required. However, no novel targets were identified in this study. We found some genes with increased copy numbers (copy number: 4–6) implying a possible resistance mechanism for BRAF-targeted therapy. However, more cases should be compiled and analyzed to confirm these data. Unlike the intrinsic and extrinsic acquired mutations in melanoma31 and NSCLC32, currently, there are not many reports on ATC. Recently, BRAF off-target resistance mechanisms in ATCs, including RAS mutations33,34 RAC1 mutations35, and copy number variations35 have been described. Further studies are warranted to understand the mechanisms of resistance to BRAF-targeted therapy in ATC.
This study provides clinical insights into the genomic landscape of ATC and identifies potential novel targets worthy of further investigation. Considering the multiple aberrant pathways present in these tumors, a multi-targeted therapeutic strategy is essential. While liquid biopsy alone may not be sufficient to identify driver mutations, it offers complementary information when the tissue is inadequate for NGS. Further studies are warranted to understand the resistance mechanisms of BRAF-targeted therapy and to find ways to overcome this resistance.