Characterization of CpG Methylation Patterns in Promoter Regions of Tumor Suppressor Genes in Colorectal Cancer Tissue from Nigerian Patients

Epigenetic silencing of tumor suppressor genes through aberrant CpG island promoter methylation is a well-established mechanism in colorectal carcinogenesis. Understanding methylation landscapes in Nigerian CRC patients is important given the potential for early detection biomarker identification in a population with limited endoscopic screening access. This study characterized CpG methylation patterns in promoter regions of selected tumor suppressor genes (MLH1, CDKN2A/p16, RASSF1A, and APC) in colorectal cancer tissue from patients at Obafemi Awolowo University Teaching Hospital (OAUTH), Ile-Ife, Osun State, Southwest Nigeria. FFPE-derived tumor and paired adjacent normal tissue from 40 confirmed CRC cases were subjected to bisulfite conversion followed by methylation-specific PCR (MSP) and quantitative bisulfite pyrosequencing for methylation quantification. Promoter hypermethylation was detected in at least one gene in 72.5% of tumor samples. MLH1 hypermethylation was observed in 35% and was significantly associated with MSI-High phenotype. CDKN2A hypermethylation was the most prevalent finding (52.5%), while APC methylation was present in 30%. Normal adjacent tissue showed methylation frequencies below 5% for all loci tested. CIMP-High phenotype, defined as methylation in three or more loci, was associated with right-sided tumor location and older age at diagnosis. These findings provide the first CpG methylation landscape data for CRC in Osun State and contribute to the evidence base for epigenetic biomarker application in Nigerian oncology. Keywords: CpG methylation, tumor suppressor genes, colorectal cancer, bisulfite pyrosequencing, Osun State.