WASHINGTON (Reuters) - MRI scans may offer a new way to detect breast cancer at its earliest stages and perhaps even prevent cancer among high-risk women, European researchers said on Thursday.

Details of a German study show that magnetic resonance imaging was better than standard mammograms, a type of X-ray, at detecting a nonmalignant tumor called ductal carcinoma in-situ, or DCIS.

This could give surgeons time to remove the lesion before it can turn cancerous.

The findings, published in the Lancet medical journal, suggest that MRI should be tested in more women to see if it should become a standard screening tool, said Dr. Carla Boetes and Dr. Ritse Mann of the Radboud University Nijmegen Medical Centre in the Netherlands.

"Although these results were unexpected, the pathophysiology of breast cancer provides ample justification for the findings," they wrote in a commentary in Lancet.

Boetes and Mann noted that autopsy results show that about 9 percent of women have undetected DCIS, and that almost all malignant breast cancer is believed to start out as DCIS.

"MRI should thus no longer be regarded as an adjunct to mammography but as a distinct method to detect breast cancer at its earliest stage," they wrote.

Dr. Christiane Kuhl, a radiologist at the University of Bonn and colleagues studied 7,319 women over five years for their study, which was also presented in June to a meeting of the American Society of Clinical Oncology.

MRI found DCIS in more than 90 percent of the 167 women with the condition, while mammograms only found 56 percent of DCIS cases.

"MRI could help improve the ability to diagnose DCIS, especially DCIS with high nuclear grade," Kuhl's team wrote.

TOO SOON TO RECOMMEND

But Debbie Saslow, director of breast and gynecologic cancer at the American Cancer Society, said it is far too soon to use MRI routinely for breast cancer screening.

"The American Cancer Society recommends that MRI screening be done annually in addition to mammography starting at age 30 for women at high risk," Saslow said in a telephone interview.

"For the most part, these are women who have had either a genetic test or found a mutation (that puts them at high risk of developing breast cancer), there is a mutation in the family, or there is a strong enough family history that would lead you to think that the risk of having a mutation is pretty high," she added.

Women who already have had breast cancer have only a moderate risk of a recurrence and are not necessarily candidates for MRI, Saslow said. The reason is that MRI is expensive -- $1,000 to $1,500 per scan -- and has a high rate of false positives, meaning it detects lesions that are harmless.

"Sometimes doctors will think they see something. With MRI it is not clear-cut," Saslow said. "Some of those women are choosing to have mastectomies."

And having an MRI does not save women from undergoing the uncomfortable mammogram process, as MRIs are always done alongside mammograms, Saslow noted. "Mammography still finds things that an MRI doesn't," she said.

Breast cancer is diagnosed in 1.2 million men and women globally every year and kills 500,000.