Just three tumor proteins can indicate lung cancer as much as a year before symptoms emerge, US researchers said on Monday in a finding that may lead to a blood test for lung cancer within five years.

They said an analysis of blood samples taken from smokers found three proteins or antigens were present in more than half of the people who later developed lung cancer. “The fact that we got a signal like this with just three biomarkers is very significant,” Dr Samir Hanash of the Fred Hutchinson Cancer Research Center in Seattle said in a statement.