Hypomethylation of ras oncogenes in primary human cancers.

We have examined the methylation status of two cellular oncogenes, c-Ha-ras and c-Ki-ras, in primary human carcinomas and the adjacent analogous normal tissues from which the tumors derived. The c-Ha-ras gene was hypomethylated in six of eight carcinomas, including five colonic adenocarcinomas and one small cell lung carcinoma, when compared to adjacent normal tissues. The c-Ki-ras gene was hypomethylated to a lesser extent in two colonic adenocarcinomas. This is the first demonstration of alterations in methylation of cellular oncogenes in human cancer.