Quantification of p16 methylation in serum DNA as a new diagnostic tool for colorectal cancer

Abstract

10050 Background: The incidence of colorectal cancer (CRC), one of the commonest malignancies worldwide, is still increasing. Despite advances in the diagnostic procedure, a large number of patients with CRC still presents with advanced disease. More sensitive and efficient diagnostic technique would make an impact on the prognosis of CRC patients through improving their compliance to the screening program, hence allowing earlier detection of the disease. To test the hypothesis that p16 methylation may serve as a marker for the diagnosis of CRC, we quantified the methylation levels of p16 in the serum DNA of CRC patients. Methods: Fresh specimens of 168 CRC and corresponding noncancerous tissues were obtained surgically at the Department of Surgery II, Nagoya University Graduate School of Medicine, together with the corresponding serum samples obtained 1 week prior to surgery. We defined the p16 methylation rate (p16 MR, in %) as follows: CM/(CM + CU) × 100%. CM is the concentration of methylated p16 sequences and CU is the concentration of unmethylated p16 sequences measured by quantitative methylation-specific PCR (Q-MSP) after bisulfite conversion. The relationship between the p16 MR and clinicopathologic findings were evaluated. Results: Aberrant p16 promoter methylation was found in 59% (99 of 168) of surgically resected CRC tissues. None of the corresponding normal tissues had methylated p16 sequences. 37% (37 of 99) serum samples of the CRC patients with tumoral p16 methylation had the same alterations. p16 MRs of 99 serum samples with tumoral p16 methylation were 0 to 68.9 (mean was 5.43±11.01). p16 MRs were significantly correlated with lymph node metastasis (P=0.001), lymphatic invasion (P=0.001) and venous invasion (P=0.020) of CRCs. p16 MRs increased significantly with tumor stage [stage I : 0.94 ± 1.68, stage II : 2.33 ± 5.19, stage III : 8.49 ± 14.22, stage IV : 10.03 ± 14.27 (P = 0.021)]. Moreover, the survival of patients with low p16 MR was significantly superior to those with high p16 MR (P=0.006). Conclusions: These results suggest that quantification of p16 methylation in the serum DNA might be a novel diagnostic tool and a prognostic factor for CRC. No significant financial relationships to disclose.