And similar questions have been raised about other mammography studies.

An expert group reviewing mammography studies decided that it could no longer say that the test prevents breast cancer deaths.

Some medical experts applauded the analysis, saying that the two investigators had pointed out serious flaws in the mammography studies and that they had appropriately emphasized that there were real risks of having the diagnostic test.

But other experts find the critique itself flawed, guilty of even worse biases than it purports to find in the original mammography studies.

"They didn't want the money to just go into mammography studies or drug trials," he said.

The research, known as the Health Insurance Plan Study, or HIP, is one of the first and largest mammography studies.

The institute will ask a panel of independent experts that advises it on that same database to look at the new mammography study, said Dr. Peter Greenwald, the institute's director for cancer prevention.

If this is the case, earlier mammography studies, conducted when treatments were less effective, would have found that screening prevents breast cancer deaths; more recent studies might not have found this effect.

Still looming, however, are unanswered questions about the original seven mammography studies that were done in decades past.

First medical applications like a pre-clinical mammography study, show great potential for the future of this technique.