Abstract 3683: Prognostic value and biological correlates of LINE1 hypomethylation in oropharyngeal cancer

Abstract Background. We have recently demonstrated that LINE-1 hypomethylation is a negative prognostic factor in oropharyngeal squamous cell carcinoma (OPSCC). HPV-positive patients with LINE-1 methylation <55% showed an almost 5-fold higher risk of death than hypermethylated once, with an overall survival as poor as HPV-negative patients. Somatic TP53 mutations are a common feature in HPV-negative OPSCC, whereas their presence has been reported in only a small subset of HPV-related OPSCC. At present, little is known about the correlation between LINE-1 methylation and p53 expression status and/or TP53 mutation in OPSCC. Methods. Since 2019, an ongoing prospective study has been enrolling patients with OPSCC in nine cancer centers in Northern Italy. HPV16 E6 DNA was quantified using real-time quantitative PCR (qPCR). LINE-1 methylation was evaluated by methylation-specific qPCR. p53 expression was detected by immunohistochemical staining. TP53 exon mutations were analyzed by Next Generation Sequencing. Results. Up to date, 134 OPSCC patients have been enrolled, including cancer of the tonsil (n=74; 55.2%), base of tongue (n=47; 35.1%), and other subsites (n=13; 9.7%). HPV16 DNA was found in 54.3% of cases: 65.7% in base of tongue, 57.1% in tonsil, and 16.7% in other subsites (p<0.001). LINE-1 methylation was higher in HPV16-positive patients (median: 55.8%, interquartile rage [IQR]: 42.5-68.5) than HPV16-negative ones (median: 40.7; IQR: 23.9-59.1; p=0.003). Nevertheless, the median LINE-1 methylation was lower (50.7%) among HPV-16 OPSCC patients who relapsed than those who did not (56.0%), thus confirming the findings previously reported. However, data from the present investigation are presently not mature to purse the study aims (median follow-up: 12.3 months). The correlation between LINE-1 hypomethylation and p53 expression has also been evaluated in OPSCC patients. p53 expression was categorized into three groups (0%, 1-49%, and ≥50%) based on the overall intensity of nuclear staining of the tumor cells. p53 was considered null, overexpressed, or wild type when its nuclear staining was 0 %, ≥50%, or ranged between 1% and 49%, respectively. Of note, the highest level of LINE-1 methylation was observed in OPSCC tissues with nuclear p53 staining between 1% and 49% (57.8%), whereas OPSCC patients with p53 expression ≥50% showed a decline of LINE-1 methylation levels (40.6; p=0.026). Interestingly, LINE-1 methylation was lower in OPSCC patients harboring TP53 mutations in both HPV16-negative (24.8%) and HPV16-positive (24.0%) OPSCC patients, even if statistical significance was reached only in the HPV-negative group (p=0.015). Conclusion. Preliminary results confirm the potential of LINE-1 methylation to identify HPV16-positive patients with poor prognosis. In addition, this study suggest that TP53 mutations might influence LINE-1 methylation, irrespective of HPV status. Citation Format: Mariateresa Casarotto, Roberto Guerrieri, Paolo Boscolo-Rizzo, Monica Schiappacassi, Sara D'Andrea, Valentina Lupato, Susanna Chiocca, Marta Tagliabue, Rita De Berardinis, Anna Menegaldo, Alice Piccinato, Paola Stritoni, Mohssen Ansarin, Doriano Politi, Giuseppe Fanetti, Giorgio Giurato, Jerry Polesel, Elisabetta Fratta. Prognostic value and biological correlates of LINE1 hypomethylation in oropharyngeal cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 3683.