Tumor Severity Linked to DNA Methylation

Researchers using a microarray technique developed to evaluate DNA methylation in tumors have found that the degree of methylation often correlates with the seriousness of the tumor, which has important implications for diagnosing cancer and predicting a patient's prognosis.

Investigators at Ohio State University (Columbus, USA; www.osu.edu) examined the methylation levels at 19 sites spanning two adjoining regions--the promoter region and the neighboring first exon--of RASSF1A genes taken from 37 primary breast tumors, seven breast-cancer cell lines, and 10 samples of normal breast tissue.

They reported in the October 1, 2003, issue of Cancer Research that genes from normal breast cells showed low-to-moderate methylation in the exon and little or no methylation in the promoter. Nearly one-third of breast tumors sampled also showed low levels of methylation in the promoter region. The remaining tumor cells and all the breast-cancer cell lines showed moderate-to-high levels of methylation in the exon and various degrees of methylation in the promoter.

"Our findings show that progressive methylation occurs in tumors from patients and support the idea that methylation begins in the exons and extends into the promoter,” said senior author Dr.Tim Hui-Ming Huang, associate professor of human cancer genetics at Ohio State University.



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