A German university hospital said on Thursday its researchers had found a way of detecting dormant cancer cells in bone marrow that can serve as an early warning sign in breast cancer cases. The hospital at Hamburg-Eppendorf said they had developed a technique that enables them to see malignant cells likely to trigger a relapse in breast cancer patients in remission. Women who have such cells in their bone marrow have a far higher risk of developing cancer again, the university said. The findings, published Thursday in the New England Medical Journal in the United States, are the result of 10 years of research in which more than 4,000 patients were studied. The technique could become widely used in three years and could one day help to prevent lung, prostate, stomach and bowel cancer, said the head of the cancer biology institute at the university, Klaus Pantel.