AbstractIntroduction:The purpose of this study is to estimate the proportion of oropharyngeal squamous cell carcinoma (OPSCC) attributable to Human Papillomavirus (HPV) in Singapore across two different time periods (2008-2011 and 2018-2021).Experimental procedures:This non-interventional, cross-sectional study involves the retrospective analysis of pre-treatment OPSCC tissue samples under Singapore General Hospital (SGH) after obtaining institutional ethics approval. Retrospective biobank records of primary OPSCC patients with archival pre-treatment tissue samples from 2008-2011 (cohort 1, n=60) and 2018-2021 (cohort 2, n=60) were retrieved. Both p16INK4a immunohistochemistry staining (IHC) and HPV-DNA testing to determine HPV genotypes for up to 32 HPV genotypes using INNO-LiPA® HPV Genotyping (Fujirebio, Japan) were performed. Data on patient demographics, tumor characteristics, and risk factors were collected from medical records and entered a case report form (CRF). Descriptive statistical analyses were performed to determine the HPV-attributable fractions (HPV-AFs) and their corresponding patient characteristics. The current abstract described the results from the cohort 1.Results:The primary outcome of this study is to determine the proportion of OPSCC cases attributable to HPV, defined by the presence of both HPV-DNA and p16INK4a positivity. The secondary outcome is to identify the distribution of HPV genotypes within the HPV-AFs of the two cohorts. In cohort 1, approximately 70% of diagnosed OPSCC cases were men, with HPV-attributable cases making up 20% of the total. Among the HPV-AFs, more than half of the HPV-positive cases were male. HPV16 (83.3%) wasthe predominant genotype in the HPV-AFs, followed by HPV26 (8.3%) and HPV58 (8.3%). The mean age of cohort 1 was 63.1 years (±11.0). Reflecting Singapore's multi-racial demographic, 68% of cohort 1 were Chinese, and 17% were Indian.Conclusion:Our study fills a critical evidence gap regarding the burden of HPV-related OPSCCs in a multi-ethnic Singaporean community. By comparing the burden of HPVs in OPSCC across the two distinct time periods, this study offers insights into the temporal changes in trends of HPV-attributable OPSCCs.Citation Format:Yew Mun Lee, Nhi Thi Mai Nguyen, Zhi Yong Lim, Zi Ting Corrina Tan, Jia Qi Gabie Chua, Yirong Dai, Xin Xiu Sam, Jia Hui Isabelle Jang, Eriko Yamada, Kok Hing Lim, Chwee Ming Lim. Temporal trends and HPV attributability in oropharyngeal cancer: A cross-sectional study in multi-racial Singapore [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 1 (Regular Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_1):Abstract nr 2311.