Tumour-Free Tissue can be Precancerous

Even normal appearing tissue
might not be free from cancer
© NCI Visuals Online

The findings, while preliminary, might have important implications for identifying breast-cancer patients at high risk of a second tumour in the same breast. Researchers looked for – and found – a chemical change called DNA methylation in healthy tissue adjacent to breast tumours.

They measured this chemical change in a gene that often becomes highly methylated in breast cancer. The gene, called RASSF1A, is a tumour-suppressor gene. Tumour-suppressor genes normally protect cells from becoming cancerous, but the gradual silencing of these genes by abnormal methylation is thought to be an early change in cancer development. In addition, the study identified three other genes that were abnormally methylated in both tumour and normal tissues.

“This is evidence that DNA methylation is a very early event in tumour development, and that genes that are methylated might serve as useful markers for early cancer detection and diagnosis,” says principal investigator Tim H-M. Huang, professor of molecular virology, immunology and medical genetics with Ohio State's Comprehensive Cancer Center.

“Our study might also help explain why, in the absence of radiation therapy, breast cancer often recurs near the site of the original tumour following a lumpectomy,” says first author Pearlly S. Yan, research assistant professor of molecular virology, immunology and medical genetics and a researcher in Huang's laboratory. As expected, tumour cells showed the highest methylation levels. But the researchers found significant methylation levels in normal tissue adjacent to the tumours in 29 patients. If the findings are verified in more patients, they might lead to a prognostic test that could help doctors estimate a woman's risk of cancer recurring near the surgical site.

MEDICA.de; Source: Ohio State University