Scientists have the first major evidence that blood tests called liquid biopsies hold promise for screening people for cancer. Hong Kong doctors tried it for a type of head and neck cancer, and boosted early detection and one measure of survival.

The tests detect DNA tumors shed into the blood. Some are used now to monitor cancer patients, and many companies are trying to develop versions for screening as possible alternatives to mammograms, colonoscopies and other such tests. The new study shows this approach can work, at least for this one form of cancer and in a country where it’s common.

“This work is very exciting on the larger scale” because it gives a blueprint for how to make tests for other tumor types such as lung or breast, said Dr. Dennis Lo of Chinese University of Hong Kong. “We are brick by brick putting that technology into place.”

He led the study, published Wednesday by the New England Journal of Medicine. Lo is best known for discovering that fetal DNA can be found in a mom’s blood, which launched a new era of non-invasive testing for pregnant women.

The study involved nasopharyngeal cancer, which forms at the top of the throat behind the nose. It’s a good test case for DNA screening because it’s an aggressive cancer where early detection matters a lot, and screening could be tried among middle-aged Chinese men where the cancer is most common.

Also, the Epstein-Barr virus is involved in most cases, so tests could hunt for viral DNA that tumors shed into the blood in large quantities, rather than rare bits of cancer cells themselves.

About 20,000 men were screened, and viral DNA was found in 1,112, or 5.5 percent. Of those, 309 also had the DNA on confirmatory tests a month later. After endoscope and MRI exams, 34 turned out to have cancer.