RUNX3 promoter methylation in colorectal cancer: its relationship with microsatellite instability and its suitability as a novel serum tumor marker.

Background/aim: RUNX3 is a novel gastric cancer tumor suppressor. RUNX3 promoter hypermethylation is associated with many types of cancer, including colorectal cancer. Furthermore, the RUNX3 promotor is one of the CpG island methylator phenotype (CIMP)-specific promotors. CIMP is a distinct phenotype associated with microsatellite instability (MSI) in colorectal cancer. In this study, the suitability of the quantitative analysis of RUNX3 promoter hypermethylation as a novel serum tumor marker was investigated. Moreover, we investigated the relationship between RUNX3 promoter methylation and MSI in colorectal cancer.

Patients And Methods: A RUNX3 real-time quantitative methylation-specific PCR (RTQ-MSP) technique we developed was used to analyze the CpG sites in the RUNX3 promoter of 119 colorectal tumors and 344 sera from colorectal cancer patients. MSI analysis of 119 colorectal tumors was performed with five microsatellite markers (BAT25, BAT26, D5S346, D2S123, and D17S250).

Results: Proximal colon tumors exhibited significantly higher RUNX3 methylation than their paired normal tissues (p=0.0438). Analysis of the clinicopathological parameters revealed that a proximal location (p=0.0054), lymphatic invasion (p<0.0001), and an advanced pathological stage (p=0.0018) were associated with significantly higher RUNX3 methylation. Assessment of the relationship between RUNX3 methylation and tumor MSI revealed 11 out of 13 tumors with high-frequency MSI (85%) were positive for RUNX3 hypermethylation, significantly more than the tumors with low-frequency MSI or which were microsatellite stable (34%, p=0.0070). In preoperative sera from 344 colorectal cancer patients, significantly higher RUNX3 methylation was associated with lymphatic invasion (p=0.0487) and an advanced pathological stage (p=0.0466). Post-operative follow-up data revealed that recurrence cases exhibited significantly higher preoperative serum RUNX3 methylation than non-recurrence cases (p=0.0003). Concomitant analysis of carcinoembryonic antigen (CEA) levels in the preoperative sera showed that 17.7% (61/344) were CEA-negative but RUNX3 methylation-positive, which means assessing both serum RUNX3 methylation and CEA should improve diagnosis of colorectal carcinoma.

Conclusion: RTQ-MSP-based quantification of serum RUNX3 methylation is useful for the detection and monitoring of colorectal cancer.