Regular blood tests can detect 86% of ovarian cancers before the point at which women normally would be diagnosed, according to a trial that could lead to national screening.
Ovarian tumours are often deadly as they are caught too late.
The first results of the 14-year trial of more than 46,000 women suggest tumours can be detected early.
However, the University College London team caution that it is still unknown whether more lives were saved.
Around 7,100 women are diagnosed with ovarian cancer and 4,200 die of the disease each year in the UK.
The cancer is difficult to pick up as symptoms, including abdominal pain, persistent bloating and difficulty eating, are common in other conditions.
Ovarian tumours spew out high levels of a chemical called CA125, which is already used as a test if patients have symptom.