But the research did give scientists a better idea of what they need to be looking for.
Current blood tests generally cannot find a tumor, in the ovary, until it's about the size of this onion.
The new research shows that to be effective in saving lives, doctors need to find tumors when they're the size of the peppercorn you see on the left of the screen.
"The good news is the long incubation period. That means an annual screening test could in theory work, if we have the right tests," said Chana Palmer Davis.
About 15,000 American women die of ovarian cancer every year.