Pediatric papillary thyroid carcinoma (PTC) present a more aggressive disease than adults, with higher risk of malignancy, higher rates of metastasis, multifocality and larger tumor sizes. We described AGK-BRAF fusion in 19% of sporadic pediatric PTC, which is associated with lung metastasis and younger age (mean 10.67 y.o.). Super-resolved three-dimensional structured illumination microscopy (3D-SIM) allows the visualization of the DNA structure inside the interphase nucleus at microscopic length scales. 3D-SIM has shown that cancer cell nuclei exhibit chromatin remodeling, with increased amount of DNA-poor spaces, which indicates a disrupted pattern in the DNA and has been associated with aggressive behavior in other tumor subtypes. In order to understand the underlying causes of the aggressiveness of pediatric PTC, we here aimed to analyze, for the first time, the DNA organization from 13 pediatric PTC patients (≤18 y.o.), using super-resolved 3D-SIM technology. A granulometry-based measurement method quantified the size distribution of DNA structure (DNA packaging) and DNA-poor spaces. We compared the granulometry for: tumor vs normal tissues; AGK-BRAF fusion (positive vs negative tumors); distant metastasis (presence vs absence); multifocal vs unifocal tumors; age at diagnosis (≤ 10 y.o. vs > 10 y.o.); tumor size ( ≤ 2 cm vs > 2 cm) and extra-thyroidal (ET) extension (presence vs absence). Nuclei from tumor cells exhibited larger DNA structures (p=0.0001) and more DNA-poor spaces (p<0.0001) than normal cells. In relation to the clinicopathological features, patients that presented distant metastasis (p=0.001), multifocal tumors (p=0.002) and > 2 cm tumors (p=0.0029), exhibited more DNA-poor spaces in their nuclei. Regarding the analyses of the AGK-BRAF fusion, borderline results were observed for both DNA structure (p=0.058) and DNA-poor spaces (p=0.053). Similar results were observed in PTC cases with age ≤10 y.o. for DNA structure (p=0.068) and DNA-poor spaces (p=0.06). No significant difference was observed for ET extension. Our preliminary data corroborate with previous studies, where tumor cell nuclei present more DNA-poor spaces than normal cells; and suggest a progressive disruption and remodeling of the chromatin in malignant cells. Interestingly, tumor cells from patients with features of poor prognosis (distant metastasis, multifocality and tumor size) can exhibit a more disrupted DNA organization, which can be related to a more aggressive behavior of the tumor. Moreover, can also observe a trend to a more disrupted chromatin organization in AGK-BRAF tumors and tumors from <10 y.o. patients, which can be associated with the aggressiveness of the disease in these cases. Further analysis are needed to better understand wether AGK-BRAF fusion is associated with poor prognosis in pediatric PTC and if it could be related to a high genomic instability caused by this fusion.

Citation Format: Luiza Sisdelli, Maria I. Cordioli, Fernanda Vaisman, Osmar Monte, Carlos Longui, Adriano N. Cury, Aline Rangel-Pozzo, Sabine Mai, Janete M. Cerutti. Alterations in nuclear DNA organization in sporadic pediatric Papillary Thyroid Carcinoma (PTC) [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 2035.