Detection of Endogenous DNA Double-strand Breaks in Oral Squamous Epithelial Lesions by P53-binding Protein 1

Background/Aim: P53-binding protein 1 (53BP1) is one of the DNA damage response (DDR) molecules. This study aimed to assess 53BP1 expression by immunofluorescence (IF) as a biomarker to differentiate between oral squamous epithelial lesions (OSELs). Materials and Methods: We analyzed 129 archival oral biopsy samples, including 18 benign squamous lesions (BSLs), 37 low-grade dysplasias (LGDs), 22 high-grade dysplasias (HGDs), and 52 oral squamous cell carcinomas (OSCCs). 53BP1 and Ki-67 expressions were examined by double IF to assess the type of 53BP1 expression. Results: We found that OSCC exhibited several 53BP1 nuclear foci, particularly high-DNA damage response (HDDR) and large focus (LF)-type, suggesting the presence of endogenous DNA double-strand breaks in the cancer genome, which could disrupt DDR and induce genomic injury. We also found a difference in 53BP1 expression between LGD and HGD, but not between BSL and LGD. Among the Ki-67-positive cells, HDDR- and LF-type expressions were higher in OSELs of higher grades. Conclusion: 53BP1 expression can be a valuable biomarker for OSELs to help estimate the grade of oral epithelial dysplasia.