In this illustration by Yi Zhang, quantum dots are depicted as gold spheres that attract DNA strands linked to cancer risks. When the quantum dots are exposed to certain types of light, they transfer the energy to fluorescent molecules, shown here as pink globes that emit a glow. This enables researchers to detect and count the DNA strands linked to cancer.

“If it leads to early detection of cancer, this test could have huge clinical implications,” said Jeff Tza-Huei Wang, an associate professor of mechanical engineering whose lab team played a leading role in developing the technique. “Doctors usually have the greatest success in fighting cancer if they can treat it in its early stage.” Wang and his students developed the test over the past three years with colleagues at the Johns Hopkins Kimmel Cancer Centre.

Stephen Baylin, deputy director of the centre and co-author of a report on the study in the journal Genome Research, said the test – which included the detection of DNA markers in the sputum from lung cancer patients – represented “a very promising platform” to help doctors detect cancer at an early stage and to predict which patients were most likely to benefit from a particular therapy. Compared with current methods, the test appeared to be more sensitive and delivered results more quickly. Said Baylin: “Th e technique looks terrific, but it still needs to be tested in many real-world scenarios. If we continue to see exciting progress, this testing method could easily be in wide use within the next five years.”

Target of the test is a biochemical change called DNA methylation, which occurs when a chemical group called methyl attaches itself to cytosine, one of the four nucleotides or base building blocks of DNA. When methylation occurs at critical gene locations, it can halt the release of proteins that suppress tumours. When this occurs, it is easier for cancer cells to form and multiply. As a result, a person whose DNA has this abnormal gene DNA methylation may have a higher risk of developing cancer.

To detect this DNA methylation, the Johns Hopkins team found a way to single out the troublesome DNA strands that have a methyl group attached to them. Through a chemical process called bisulfite conversion, all segments that lack a methyl group are transformed into another nucleotide, after which another lab process is used to make additional copies of the remaining target DNA strands that are linked to cancer.