Abstract 980: Genomic characterization of lymph node metastases in papillary thyroid carcinoma following the Chernobyl accident reveals an expression profile specific to metastatic process

Following the Chernobyl nuclear power plant explosion in Ukraine in 1986, increased childhood exposure to radioactive iodine (131I), which occurred primarily through contaminated food sources, has been consistently associated with increased risk of developing papillary thyroid carcinoma (PTC). Increased frequency of cervical lymph node metastases (LNM) is well recognized in pediatric PTC, including pediatric cases following the Chernobyl accident. We recently leveraged the collection of fresh-frozen tumor tissues from the Chernobyl Tissue Bank to conduct a genomic landscape analysis of 440 cases of PTC that provided new insights into radiation-related molecular characteristics of PTC occurring after the accident (Morton et al., Science 2021). Here, we extend that study to conduct a genomic landscape analysis of LNMs for a subset of 48 PTC cases to investigate the specific genomic alterations occurring in LNM. The analysis set comprised 144 samples, including fresh-frozen treatment-naïve primary and LNM PTC tumor samples as well as matched normal tissue or blood. Overall, the mutational load was highly concordant between primary and metastatic PTC. On average, 50% of somatic single nucleotide variants and 97% structural variants were shared between primary and metastatic PTCs. In contrast, the burden of somatic copy number alterations (SCNA) between primary tumor and LNM pairs was less concordant, particularly for copy number gains, whereas most of the copy number loss was found to be shared between matched pairs. PTC is usually driven by one driver mutation, most often involving the mitogen-activated protein kinase (MAPK) pathway. All driver mutations were shared between primary and metastatic PTC and were clonal; thus, no additional driver mutations were detected in metastatic PTC. Notably, however, the matched pairs in this study disproportionately had fusion drivers (77%), whereas only 23% of the drivers were BRAF V600E and none were RAS mutations. Transcriptome analysis revealed differentially expressed genes (DEGs) in metastatic PTC compared to primary PTC; three-quarters of the DEGs were overexpressed in metastatic PTC. Half of the LNM overexpressed DEGs were members of the HOXC family, which has been linked with epithelial-mesenchymal transition in cancer progression. There was also reduced expression in LNM for the DLX family, which relates to TGF-beta signaling. Our findings did not reveal a relationship between radiation dose and expression profiles in the LNM, comparable to our findings for the primary PTCs. We still observe that the efficiency of the radiation-induced PTC is paramount and subsequent events are directly related to the drivers in the MAPK pathway. For the cervical LNMs, we observed expression profiles not observed in the primary PTC that could give new insights into PTC local metastases. Citation Format: Olivia W. Lee, Danielle M. Karyadi, Chip Stewart, Tetiana I. Bogdanova, Jieqiong Dai, Stephen W. Hartley, Sara J. Schonfeld, Vidushi Kapoor, Marko Krznaric, Meredith Yeager, Amy Hutchinson, Belynda D. Hicks, Casey L. Dagnall, Julie M. Gastier-Foster, Jay Bowen, Mitchell J. Machiela, Elizabeth K. Cahoon, Kiyohiko Mabuchi, Vladimir Drozdovitch, Sergii Masiuk, Mykola Chepurny, Liudmyla Y. Zurnadzhy, Amy Berrington de González, Gad Getz, Gerry A. Thomas, Mykola D. Tronko, Lindsay M. Morton, Stephen J. Chanock. Genomic characterization of lymph node metastases in papillary thyroid carcinoma following the Chernobyl accident reveals an expression profile specific to metastatic process [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 980.