Prognostic value of p16INK4a and p14ARF gene hypermethylation in human colon cancer.

The INK4a/ARF locus (9p21) encodes two unique and unrelated cell cycle regulators, p16INK4a and p14ARF. This study was performed to evaluate the methylation status of p16INK4a and p14ARF genes, as well as its association with p16 and p53 expression, microsatellite instability (MI) status, and various clinicopathologic parameters in sporadic colorectal cancer. Sixty-five cases of primary colorectal adenocarcinoma with a series of clinicopathological parameters were obtained. We performed methylation-specific PCR of p16INK4a and p14ARF genes in colorectal cancer paraffin blocks with its paired normal samples, as well as immunohistochemical stainings for p16 and p53, and MI analysis. Aberrant methylations of p16INK4a and p14ARF gene were present in 21 (32.3%) and 33 (50.8%) out of 65 cases, respectively. p16INK4a aberrant methylation was correlated with p16 negativity (P=0.021) and p53 overexpression (P=0.007). p16INK4a aberrant methylation was more frequently present in poorly differentiated adenocarcinomas (P=0.002). Aberrant methylation of p14ARF gene occurred more frequently in patients under 50 years of age and in left-sided colon cancers, and was not statistically significant. Compared with the group with simultaneous absence of methylation in both promoters, the group showing concomitant alterations in both p16INK4a and p14ARF genes (n=10) more frequently presented lymph node metastasis (P=0.020) and higher tumor grade (P=0.014). There was no correlation between p16INK4a and p14ARF gene hypermethylation or MI status. This study suggests that simultaneous hypermethylation of both p16INK4a and p14ARF genes is greater prognostic value in sporadic human colorectal cancer.