Image courtesy of the University of Washington Breast Imaging program
A new study, using a built-in but little-understood visual byproduct of MRI breast imaging, offers the possibility of nailing down a woman’s “true risk” of breast cancer – for a woman already at high risk of the disease, that is.
One in eight U.S. women will develop breast cancer over her lifetime, according to the National Cancer Institute, meaning the average woman has about a 12 percent chance of getting the disease. Women termed “high risk” are those with a 20 percent or greater lifetime chance of breast cancer.
But most women, and their doctors, are left without much information beyond that high- versus normal-risk status, said Dr. Habib Rahbar, a radiologist at Seattle Cancer Care Alliance, Fred Hutchinson Cancer Research Center’s treatment arm, and one of the study’s investigators. It turns out being dubbed high risk includes a wide range of probabilities of actually developing the disease.
“Twenty percent to 100 percent is obviously quite a great range, so the ability to further determine which patients are most likely to develop breast cancer is really significant,” Rahbar said.
Knowing where a woman falls within that wide range would help her doctors better guide her screening and treatment options, he said.
Rahbar and his colleagues found that a feature of breast MRI imaging that previously was not known to have clinical implications can in fact help pinpoint the chances of developing breast cancer among those at high risk. That tool could lead to a more precise cancer-risk assessment. Dr. Brian Dontchos, a Seattle radiologist and study investigator, presented the findings today at the Radiological Society of North America’s annual meeting in Chicago.
MRI might predict cancer before it starts
Their study suggests that breast MRI, a technique commonly used for screening high-risk women, could be used not only to catch breast cancer, but to predict it before it starts.
To look for breast cancer, radiologists compare MRI images of the breast before and after injecting a contrast agent into the patient’s bloodstream; tumors glow bright when the dye pumps through the breast’s blood vessels. But it turns out for some women, normal parts of their breasts light up too. That background glow, which radiologists term “background parenchymal enhancement,” or BPE, has largely been ignored except as an inherent artifact of some MRIs.
“No one really understood whether BPE had any clinical implications,” Rahbar said.
The researchers tracked 487 high-risk women who received screening MRIs at SCCA. Over the six years of the study, 23 of those women developed breast cancer. The researchers compared those women with an age-matched group of cancer-free women from the study and found that those who went on to develop cancer had higher BPE levels on their initial MRI exam than those who didn’t develop breast cancer.
The researchers don’t yet know whether BPE could also predict breast cancer risk in the general population. They hope to examine that question in future research, but to do so would be a much larger and more costly undertaking, Rahbar said, in large part because insurance companies don’t currently cover the cost of MRI screening for average-risk women.
“This opens up an avenue in imaging that hasn’t been well explored,” added Dr. Savannah Partridge, a co-investigator of the study and breast imaging expert at SCCA and UW Medicine.
A powerful marker of cancer risk
Current methods to calculate breast cancer risk are based on studies of populations, Rahbar said. That’s a problem when it comes to assessing an individual woman’s risk or making medical decisions based on that risk.
Doctors use a woman’s age, family history and facts about her menstrual cycle and whether she’s had children (both of which give clues as to how much estrogen has been kicking around in her body) to determine breast cancer risk.
“The problem with those factors is that they’re really common in the general population, and they’re individually very weak predictors of whether a woman will develop breast cancer or not,” Rahbar said. “[BPE] could be a very powerful individual marker.”
If doctors can uncover a woman’s true risk of breast cancer, they can help her make concrete decisions about managing that risk. Since nearly all radiologists experienced in breast MRI understand how to identify BPE when performing breast MRIs, any facility that performs screening MRIs could potentially use this tool, Rahbar said.
Depending on how great a woman’s chances of developing the disease, her options would range from increased screening to taking a daily dose of a cancer-preventing drug, such as tamoxifen, to a preventive double mastectomy. Some of those choices would be more appropriate for women at very high risk of cancer but possibly not for those just over the borderline of high risk, Rahbar said.
“We don’t want to provide those sorts of recommendations to patients without having a really clear idea what their risk is rather than this huge range,” he said.
A fertile ground for cancer growth
What BPE is, and why it could herald cancer’s arrival, remains a bit mysterious. Since it’s related to blood flow, scientists feel it reflects some kind of activity in the breast.
BPE is also loosely related to breast density, another known risk factor for breast cancer. Breast density refers to how much of a woman’s breasts are made up of fat versus glandular and connective tissue. The less fat, the higher the density. A woman with very low density is unlikely to show any of this background signal on an MRI, Rahbar said, but not all women with dense breasts will have high BPE.
The researchers also found that among high-risk women, breast density was an unreliable predictor of breast cancer risk and that BPE may prove to be a better tool for measuring such a woman’s chances of getting breast cancer.
As for why BPE correlates with cancer risk, that’s unknown, but the researchers hypothesize that it’s related to the pro-cancer effect of certain circulating hormones. .In pre-menopausal women, the MRI signal rises and falls with the ebbs and flows of estrogen in the menstrual cycle. Women with lower estrogen levels – post-menopausal women and those taking the hormone suppressor tamoxifen – have low BPE.
Because lifetime estrogen exposure is itself a risk factor for breast cancer, Rahbar thinks high BPE might be a way to visualize an estrogen-sensitive – and thus more cancer-prone – breast.
“In many ways, we feel like we may be looking at areas within breasts that are very fertile for a cancer to grow,” he said.
The International Society for Magnetic Resonance in Medicine and the Roger E. Moe Fellowship in Multidisciplinary Breast Cancer Care funded the research.
Editor’s note: SCCA is recruiting high-risk women with dense breasts for a clinical trial that aims to improve breast cancer detection among this group.
Solid tumors, such as those of the breast, are the focus of Solid Tumor Translational Research, a network comprised of Fred Hutchinson Cancer Research Center, UW Medicine and Seattle Cancer Care Alliance. STTR is bridging laboratory sciences and patient care to provide the most precise treatment options for patients with solid tumor cancers.
Rachel Tompa is a former staff writer at Fred Hutchinson Cancer Research Center. She has a Ph.D. in molecular biology from the University of California, San Francisco and a certificate in science writing from the University of California, Santa Cruz. Follow her on Twitter @Rachel_Tompa.
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