Tumor p16 INK4 gene expression and prognosis in colorectal cancer

Abstract

Hypermethylation of the tumor suppressor gene p16 INK4 (p16) promoter is associated with worse prognosis in colorectal cancer (CRC). In the present study, it was investigated whether p16 mRNA expression correlates with the methylation of its promoter, and whether it influences prognosis in patients with CRC. DNA and RNA were extracted from 101 resected tumor specimens. A MethyLight assay was used to quantify p16 methylation in terms of percentage of methylated reference (PMR), and the expression of p16 mRNA was measured using reverse transcription-polymerase chain reaction. Associations between p16 methylation or mRNA expression and patient survival were evaluated using Kaplan-Meier analysis and Cox proportional hazards regression. p16 methylation was detected in 67 cases (66.3%) and the median PMR value was 0.344 (range, 0.00-468.6). Using a cut-off PMR value of 4, high p16 methylation was observed in 18 cases (17.8%). No significant association was observed between p16 methylation level and patient prognosis. As expected, a significant inverse association was observed between p16 methylation and mRNA expression (P=0.034). Amongst the 83 cases with low p16methylation, a significantly worse outcome was identified in patients expressing high p16 mRNA expression levels (P=0.026). Multivariate analysis identified that p16 mRNA expression was an independent prognostic factor for worse survival (P=0.011). These results suggested a paradoxical association between high levels of p16 mRNA expression in the tumor and worse prognosis in patients with CRC.