Ductal carcinoma in situ sometimes can turn into invasive breast cancer, but there's currently no test that can tell when it's dangerous and when it's not. Steve Gschmeissner/Science Photo Library/Corbis hide caption

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Lateral mammogram showing a tumor iStockphoto hide caption

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TV host Samantha Harris says she will have a double mastectomy after being diagnosed with breast cancer. But the surgery doesn't eliminate cancer risk. Jordan Strauss/Invision/AP hide caption

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