Genetic alterations in colorectal cancers with demethylation of insulin-like growth factor II

Loss of genomic imprinting is an epigenetic alteration of some cancers involving the absence of parental origin-specific expression of imprinted genes. Loss of genomic imprinting of insulin-like growth factor II is often detected in colorectal cancer. However, the genetic alterations accompanied by colorectal cancer with insulin-like growth factor II loss of genomic imprinting have not been fully determined. Genomic DNA samples were collected from 52 colorectal cancer tissues and analyzed. The loss of insulin-like growth factor II genomic imprinting status was determined by assessing the demethylation of the insulin-like growth factor II differentially methylated region using bisulfite sequencing. The molecular signatures were also examined: genetic mutations of KRAS, BRAF, and PIK3CA; the expression of CTNNB1 and TP53; and microsatellite instability status. Several cases of colorectal cancer with normal insulin-like growth factor II imprinting were located in the distal colon; in contrast, colorectal cancer with loss of genomic imprinting tended to be found in the proximal colon (22.7 versus 56.6%). The PIK3CA gene mutation was highly detected in normal imprinting tumors compared to colorectal cancers with insulin-like growth factor II loss of genomic imprinting (27.3% versus 6.7%). In multivariate analysis of these clinicopathologic and molecular factors of tumors, statistically significant relationships were observed among the proximal location of the tumor (odds ratio, 12.9; 95% confidence interval, 1.52-110.13), PIK3CA genetic mutation (odds ratio, 0.082; 95% confidence interval, 0.01-0.73), and insulin-like growth factor II genomic imprinting status. Our findings indicate that colorectal cancers with demethylation of the insulin-like growth factor II gene are distinct from normal imprinting tumors, both in clinical and genetic features.