Liquid Biopsy

Fast DNA-sequencing machines are leading to simple blood tests for cancer.

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A blood test to catch cancer early.

Cancer kills some eight million people a year around the world.

Everything about China is big, including its cancer problem. In some wealthier cities, like Beijing, cancer is now believed to be the most frequent killer. Air pollution, high rates of smoking, and notorious cancer villages scarred by industrial pollution are increasing death rates around the country. Liver cancer in particular is four times as prevalent as it is in the West, in part because one in 14 people in China carry hepatitis B, which puts them at risk. Of all the people worldwide who die of cancer each year, some 27 percent are Chinese.

In December, I traveled by metro from Shenzhen to Hong Kong. There I had arranged to meet Dennis Lo, a doctor who has worked for nearly 20 years on a technique called the liquid biopsy, which is meant to detect liver and other cancers very earlyeven before symptoms ariseby sequencing the DNA in a few drops of a persons blood.

Lo appeared fastidiously dressed as usual in a sharp blazer, a habit that called to mind formal dinners at the University of Oxford, where he studied in the 1980s. He is well known for having been the first to show that a fetus sheds bits of its DNA into the bloodstream of its mother. That finding, first made in 1997, has in recent years led to a much safer, simpler screening test for Down syndrome. By now more than one million pregnant women have been tested.

Today Lo is competing with labs around the world to repeat that scientific and commercial success by developing cancer screening tests based on a simple blood draw. Thats possible because dying cancer cells also shed DNA into a persons blood. Early on, the amount is vanishingly smalland obscured by the healthy DNA that also circulates. That makes it difficult to measure. But Lo says the objective is simple: an annual blood test that finds cancer while its curable.

Cancers detected at an advanced stage, when they are spreading, remain largely untreatable. In the United States, early detection is behind medicines most notable successes in applying technology to cut deaths from common cancers. Half of the steep decline in deaths from colorectal cancer is due to screening exams like colonoscopies.

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