Scientists are reporting progress on a blood test to detect many types of cancer at an early stage, including some of the most deadly ones that lack screening tools now.Many groups are working on liquid biopsy tests, which look for DNA and other things that tumors shed into blood, to try to find cancer before it spreads, when chances of cure are best.In a study Thursday in the journal Science, Johns Hopkins University scientists looked to see how well their experimental test detected cancer in people already known to have the disease. The blood tests found about 70 percent of eight common types of cancer in the 1,005 patients. The rates varied depending on the type — lower for breast tumors but high for ovarian, liver and pancreatic ones.In many cases, the test narrowed the possible origin of the cancer to one or two places, such as colon or lung, important for limiting how much follow-up testing a patient might need.