The reviewers “could not find any studies where they could clearly show whether supplemental MRI or supplemental ultrasound reported evidence of less progression to advanced cancer,” says John Wong, professor of medicine at Tufts University School of Medicine (in Massachusetts, USA) and vice president of the USPSTF, who helped develop new breast cancer recommendations that also lowered the age at which most women should begin biannual screening mammograms from 50 to 40 years.
Dense breasts contain higher levels of fibrous and glandular tissue along with the fat that gives breasts their size and shape. The issue of complementary screening is important because higher density is associated with up to a six-fold increased risk of developing breast cancer.
When a mammogram is performed on dense breast tissue, “there’s more interference,” says Kelsey Hampton, education director for the Dallas-based nonprofit Susan G. Komen Foundation, dedicated to breast cancer research and advocacy. . “It’s like trying to look through a glass jar full of clear water versus a glass jar full of water with ice cubes. You still see things, but it’s harder to see them with the same level of detail.” Still, she says, mammograms are important for these women.
Many gynecologists routinely prescribe complementary ultrasounds or MRIs along with mammograms in women diagnosed with dense breasts. The new “insufficient evidence” or “I” rating given by the task force does not mean that no women will benefit from supplemental screening.
“We urgently call for more research into whether and how additional screening can help women with dense breasts detect cancer earlier,” the final recommendation says.
But the classification is likely to confuse doctors about whether they should continue prescribing the additional test and whether some insurers might stop covering it, says Wendie Berg, a distinguished professor of radiology at the University of Pittsburgh who disagrees with the group’s position. of work. Berg calls the task force’s I rating “astonishing,” as she believes the current evidence is sufficient to recommend these tests.
Increasing confusion: Starting in September, the US Food and Drug Administration (FDA) will require that all women getting a mammogram be notified which of four density levels describe their breasts and to be warned that “in some people with dense tissue, other imaging tests besides mammography can help detect cancers.”
The first studies on additions to mammograms date back more than 20 years. However, too little research has been done in the intervening decades to convince the USPSTF that additional screening is worthwhile.
However, compared to many other medical conditions, breast cancer is a well-funded field of research. The disease received more funding globally than other types of cancer between 2015 and 2020, about $2.7 billion, according to a study published in the journal The Lancet. Each year, the U.S. National Cancer Institute devotes more than $500 million to breast cancer research, supplemented by funding from nonprofit organizations like Komen, which has supported more than 550 clinical trials. costing more than $1 billion since 1982, according to the organization.
According to the study of The Lancet, most of these funds do not go toward screening research. The vast majority went to the study of cancer biology, followed by drug treatment, immunotherapy and surgery.
To make their assessment, the working group evaluated a handful of randomized screening trials that tracked the impact of supplemental screening.
In one, for example, Japanese researchers studied a cohort of 70,000 women with all levels of breast density and randomly assigned half of them to a group that received screening ultrasound plus mammography or mammography alone. In the months following a round of screening, they found no differences in so-called interval cancers, a measure used to demonstrate the potential benefit of a screening tool. This study is ongoing, and additional rounds of screening could yield different results.
Researchers in the Netherlands are also conducting a multi-year study. To date, they have published the results of two rounds of MRI testing that included nearly 3,500 women with extremely dense breasts whose mammograms came back negative. In the second round, six more cancers were detected per 1,000 women. But the test also flagged 26 cases that weren’t potential cancers. These false positives require unnecessary additional procedures, resulting in increased anxiety. This rate was lower than the false positive rate of the first round, in which there were almost 80.
According to Wong, increased detection rates alone do not indicate that the techniques are beneficial. For example, if the cancers detected by supplemental screening are slow growing, they probably could be treated just as effectively if they had been detected at the next scheduled mammogram.
“When you look more, you see more,” says Wong; “But is there a definitive benefit, where patients can clearly live longer from that positive supplemental screening? We haven’t gotten there.”
Not everyone agrees that the evidence is inconclusive. The European Breast Imaging Society advocates supplemental screening with MRIs every two to four years for women with extremely dense breasts. For its part, the American College of Radiology recommends that women with a higher than average risk of breast cancer undergo annual mammograms and complementary MRIs.
Berg was disappointed that the task force excluded some studies from its evaluation because they were not randomized controlled trials. One of the excluded studies included more than 1,000 women with dense breasts who underwent two annual mammograms supplemented by an MRI. In that research, four additional cancers were detected with MRI, many of them invasive. Other studies found that screening ultrasounds detect an average of two to three additional cancers per thousand, many of them invasive.
Some women will receive false-positive results that will require unnecessary follow-up, she admits. But in a review published in 2019 she claims that careful training of technicians along with increasing use of supplementing radiologists’ readings with artificial intelligence can minimize this rate.
The USPSTF states that to potentially change its assessment of additional screening in the next review cycle (likely in about five years) more studies are needed that report on health outcomes such as quality of life and mortality, especially those conducted in settings applicable to primary care in the US.
Additional years of screening from ongoing major studies may provide the data the task force needs, Wong says.
In the meantime, women should talk to their doctors to find out both their level of breast density and their overall risk of breast cancer, Hampton says. Density can vary over time, especially with age, weight changes, pregnancy, breastfeeding, or hormonal therapy during menopause.
People with dense breasts should talk to their doctor about prescribing a test that complements mammography, Berg says. MRI is more effective than ultrasound, but the technology is not as widespread and the cost to the patient may be higher. Some people refuse MRI tests for other reasons. In the Dutch study they were offered free of charge, but 40 percent of women rejected them, citing inconvenience, concern about the injection of the needle that inserts the contrast material, and claustrophobia when being in the machine.
In the US, insurance coverage of mammograms varies depending on state law. Some observers are concerned that insurers could use the USPSTF I classification as justification for the change.
“There is a possibility that by classifying these ancillary services as inconclusive, insurance companies may stop covering them,” Hampton says.
Berg believes that early detection of breast cancer is so important that women with dense breasts should not be deterred by the USPSTF classification. “A woman should have enough information to make her own decision and ask her doctor for the prescription if she wants it,” she says: “That’s the bottom line.”