Detecting breast cancer at earlier stages can increase survival outcomes and require less-aggressive therapies, but mammography, while widely available and relatively inexpensive, is known to be less sensitive as a screening modality for women with dense breasts, said Savannah Partridge, PhD, a professor of radiology and the associate director of cancer imaging for the Seattle Cancer Care Alliance at the University of Washington in Seattle.
In the U.S., women with dense breasts are encouraged to seek supplemental screening in addition to mammography, she noted.
Results of large screening studies have shown MRI to have much higher sensitivity than mammography for detecting breast cancer, particularly in women with dense breasts. Moreover, emerging evidence suggests the breast cancers missed by mammography tend to more often be highly vascularized, higher-grade cancers in need of more aggressive therapies.
"So why are we not using breast MRI in more women?" asked Dr. Partridge, noting current issues such as the time and expense of the exam, the false-positive rate, and the need for contrast. "We know that MRI has a very high sensitivity for detecting breast cancer, and it could be a really useful screening tool. But these disadvantages limit its practicality to extending toward more women."
Currently, MRI is primarily recommended for women who have a very high risk, regarded as having a greater than 20% lifetime risk, and for preoperative assessment in women who have a cancer diagnosis.
"It has not been deemed to be cost-effective for women who have lower than 20% lifetime risk because the odds of them having cancer is lower," Dr. Partridge said. "If we could bring the costs down, we could think about being able to offer it [to women] more, like ultrasound or other supplemental screening tools."
Women in the U.S. who have dense breasts but are not at high risk currently may have to pay out of pocket to undergo breast MRI for supplemental screening, as their insurance will typically not cover it, she noted.
"The best way to reduce the expense is to reduce the long examination time," said Dr. Partridge, pointing to the availability of an abbreviated MRI protocol, as first introduced in Germany in 2014 by Kuhl et al (Journal of Clinical Oncology, 2014, Vol. 32:22, pp. 2304-2310), that offers great practicality by significantly reducing the time to acquire and interpret images and could potentially be offered at significantly lower cost than the full breast MRI protocol.
To reduce false positives (associated with the full protocol), which also add downstream costs because of the need for biopsy, Dr. Partridge highlighted the potential of new ultrafast dynamic contrast-enhanced (DCE) and diffusion-weighted imaging (DWI) techniques for improved characterization of suspicious breast lesions, with preliminary results from the ECOG-ACRIN 6702 DWI multisite trial suggesting the biopsy rate could be reduced by more than 20% without any cancers going undetected.
To get around the reliance on a gadolinium-based contrast agent, Dr. Partridge proposed using diffusion-weighed imaging. "Gadolinium is our main means for detecting cancer in breast MRI," she said. "We rely on areas that are enhancing on DCE for identifying the malignancy. However, we know that diffusion-weighted imaging is the main other MR sequence that can show breast cancer without injecting the contrast agent."
Research is now being conducted to evaluate if malignancies that have been found with DCE MRI could have been found with DWI, noted Partridge, pointing out that DWI may have limitations.
"With DCE, you are looking at areas of altered vascularity, which is a characteristic of breast cancers," she said. "With DWI, we are looking at differences in micro structure and cell density. We think it [DWI] may have reduced performance in breast cancers that are more diffusely growing or in very small lesions because DWI inherently has poorer spatial resolution than DCE MRI."
Dr. Partridge emphasized that new advances in DWI techniques would likely improve spatial resolution and sensitivity of the technique in the near future.
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