New DNA tests aim to detect colon cancer early

A new generation of DNA tests could offer early detection of colon cancers as well as precancerous polyps--even those not picked up by a colonoscopy. 

Researchers began measuring mutations in DNA a few years ago to assess a patient's risk for colon cancer, and while they were slightly better than the traditional test of detecting blood in the stool in detecting precancerous polyps, improvements were needed. This new generation of tests in development depend on a different process in cancer cells.

All cells switch off the genes they don't need by attaching small chemicals called methyl groups to certain sites along their DNA. In cancer cells, there is generally less methylation than usual, except for certain regions where the methylation process is taken to excess, the New York Times notes. Methylation markers are clinically relevant for the detection of colorectal cancers and precancers and are typically present more frequently than individual DNA mutation markers. As a result, fewer methylation markers are required to detect the cancers.

Madison, WI-based Exact Sciences (Nasdaq: EXAS) is developing a colon cancer test based on highly methylated DNA. Late last month, the company presented data at the American Association of Clinical Chemistry demonstrating that its methylation-specific technology detected 100 percent of colorectal cancers and precancers at a specificity cutoff of 100 percent in a preliminary study with colorectal tissue. The company recently obtained an exclusive license for up to two DNA methylation biomarkers to use in stool-based detection of colon cancer from Belgium's OncoMethylome Sciences S.A. Exact has said it plans to run a pre-clinical study in the second half of 2010 and hopes to have the test in clinical trials by the third quarter of 2011, the Milwaukee Journal Sentinel reported late last month.

While Exact's results are promising, Dr. David Ransohoff, an expert on colon cancer screening at the University of North Carolina, cautions that we are still at an early point in development. "This is neat and it's promising," he tells the NYT. "But we've been down this road before and we need to be hopeful without being carried away."

- check out Exact Sciences' release 
- see the NYT story
- here's the Journal Sentinel story

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