Scientists have completed a major analysis of the genetics of breast cancer and find four major classes of the disease. They hope their work will lead to more effective treatments.

The new findings offer hints that one type of breast cancer might be vulnerable to drugs that already work against ovarian cancer.

The study appeared online Sunday in the journal Nature. It's the latest example of research into the biological details of tumors, rather than focusing on where cancer arises in the body.

The hope is that such research can reveal cancer's genetic weaknesses that someday can be targeted by drugs, even some already in use.

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