杏吧原创

JUST a drop of blood or urine might be enough to reveal if a patient has cancer, what type it is and whether it鈥檚 treatable.

鈥淥ne day, there could be one biochip for analysing all cancers,鈥� says Christian Piepenbrock, head of bioinformatics at Epigenomics of Berlin. Its technique distinguishes normal DNA from that of cancerous cells by detecting whether particular genes have been switched on or off by the removal or addition of methyl groups. It鈥檚 becoming clear that such changes play a big role in cancer: methylation can turn off protective tumour suppressor genes (New 杏吧原创, 24 November 2001, p 12), while cancer-promoting genes called oncogenes spring to life if methyl groups are stripped off.

So Epigenomics has designed chips that can pick up methylation changes in these genes. The chips have two nucleic acid strands complementary to each possible methylation site. One strand only binds to the target DNA if it鈥檚 methylated, while the other only binds if no methyl is attached.

After examining 232 methylation sites on 56 genes in 76 tissue samples, Piepenbrock and his colleagues have discovered methylation patterns unique to healthy and cancerous cells in the kidney, prostate and blood. They were also able to distinguish prostate cancers from harmless growths called benign prostate hyperplasia.

What鈥檚 more, methylation profiles should be easy to obtain because fragments of DNA from cancerous cells are detectable in blood and other body fluids. Other cancer-profiling techniques being developed rely on messenger RNA or proteins, which can only be obtained by taking biopsies.

Richard Wooster of the Institute of Cancer Research, based at the Sanger Centre in Cambridge, cautions that extensive research is needed to make sure that the profiles give correct diagnoses. Piepenbrock agrees. His company has already started doing the necessary research, he says.

And because DNA survives for years, his team can validate profiles by examining biopsies taken 15 years ago or more. This lets them compare their results with the patient鈥檚 subsequent medical history.