Background: p16 (CDKN2A/Ink4a) is a cyclin-dependent kinase inhibitor and functions as a tumor suppressor. CDKN2A promoter methylation and gene silencing are associated with the CpG island methylator phenotype (CIMP) in colorectal cancer. However, prognostic significance of CDKN2A methylation or loss of p16 expression independent of CIMP status has not been studied.

Patients and Methods: Utilizing 940 colorectal cancers (stage I-IV) in two independent cohort studies (the Nurses’ Health Study and the Health Professionals Follow-up Study), we quantified DNA methylation in the CDKN2A promoter real-time PCR (MethyLight) and detected hypermethylation in 269 tumors (29%). By immunohistochemistry, we detected loss of p16 (CDKN2A) expression in 25% (200/804) of tumors. We also analyzed DNA methylation in LINE-1 and 7 other CpG islands (CACNA1G, CRABP1, IGF2, MLH1, NEUROG1, RUNX3 and SOCS1); microsatellite instability (MSI); KRAS, BRAF and PIK3CA mutations; and expression of β-catenin, p53, p21, p27, cyclin D1, fatty acid synthase (FASN), and cyclooxygenase-2 (PTGS2, COX-2).

Results: In multivariate logistic regression analysis, CDKN2A methylation was independently associated with CIMP-high [adjusted odds ratio (OR) 41.6; 95% CI, 21.6-80.0; vs. CIMP-0], CIMP-low (adjusted OR 5.66; 95% CI, 3.75-8.53; vs. CIMP-0), and COX-2 negativity (adjusted OR 0.46; 95% CI, 0.29-0.74; COX-2 -positive vs. negative). Both CDKN2A promoter methylation and loss of p16 were significantly associated with high overall mortality in univariate Cox regression analysis [hazard ratio (HR), 1.31; 95% CI, 1.07-1.60; p=0.009 (CDKN2A methylation), HR, 1.30; 95% CI, 1.03-1.63; p=0.026 (loss of p16)] but not in multivariate analysis [HR, 0.79; 95% CI, 0.57-1.09; p=0.14 (CDKN2A methylation), HR, 1.00; 95% CI, 0.79-1.27; p=0.98].

Conclusion: Both CDKN2A promoter methylation and loss of p16 expression in colorectal cancer are not independently associated with patient survival. However, CDKN2A promoter methylation is independently associated with CIMP and COX-2 negativity.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 4639.