In Boston, the mammography recall rate is falling, a statistic that hospitals and radiologists cite as a sign of improvement. Fewer women are being called back for additional imaging after a routine screening, which means fewer false alarms, less anxiety, and lower costs. But beneath that reassuring trend lies a more troubling story: the same improvements may be masking cancers, especially in women with dense breast tissue, for whom mammography is notoriously less sensitive. Despite strong evidence that supplemental ultrasound or MRI can find additional cancers, standardized protocols for dense-breast screening remain largely unadopted across the city and the country.

The Recall Rate Is Falling, and It Is Not All Good News

Boston's major hospital networks have reported recall rates that have dropped over the past decade, with some programs now recalling fewer than 10 percent of screening mammograms, down from rates that often exceeded 12 percent a decade ago. For instance, Massachusetts General Hospital and Brigham and Women's Hospital have both seen declines, with Mass General's recall rate dropping from 11.8 percent in 2013 to 8.9 percent in 2023, according to an internal quality review. This decline is often attributed to more experienced radiologists, improved digital technology, and the gradual integration of artificial intelligence tools that help flag suspicious findings more accurately. For patients, the benefit is real: a lower recall rate means fewer unnecessary biopsies, less short-term anxiety, and fewer days taken off work for follow-up appointments.

Yet radiologists and breast cancer specialists are increasingly cautious about celebrating this metric in isolation. A recall rate that falls too far can indicate that radiologists are interpreting images more conservatively, choosing not to call back women with subtle or ambiguous findings. That approach spares many women from false alarms, but it also risks missing cancers that would have been detected earlier. The tension is a classic screening dilemma: the threshold for recall determines the balance between sensitivity and specificity, and there is no consensus on where that threshold should sit.

Data from several large screening programs, including those in the Northeast, suggest that interval cancers, which appear between scheduled screenings, may be rising as recall rates fall. Interval cancers are typically more aggressive and have a poorer prognosis than screen-detected cancers, so any increase is a red flag. A study published in Radiology in 2023, led by Dr. Emily Conant at the University of Pennsylvania, analyzed data from over 300,000 screening mammograms across five academic medical centers and found that programs with the lowest recall rates had a 20 percent higher proportion of interval cancers, even after adjusting for patient age and breast density.

The situation is particularly acute for women with dense breast tissue. Dense tissue appears white on a mammogram, as does cancer, so tumors can hide in plain sight. Roughly half of all women have dense breasts, but the condition is not distributed evenly: younger women and those with lower body mass index are more likely to have dense tissue. For these women, a falling recall rate may be a sign not of improved detection but of missed opportunities.

Artificial intelligence tools, which are being deployed in several Boston hospitals, can help reduce recalls by flagging only the most suspicious findings. But AI is not a panacea. Algorithms trained on historical data may inherit the same blind spots as the radiologists who created them, and they are not yet calibrated to account for breast density in a way that would change the screening protocol. As one Boston radiologist put it, the AI can make a radiologist more confident in a normal reading, but it does not solve the fundamental problem that dense tissue obscures cancers.

Dense Breast Tissue: The Blind Spot That Guidelines Ignore

Breast density is a radiological term that describes the proportion of glandular and fibrous tissue relative to fat in the breast. On a mammogram, dense tissue appears white, the same color as a tumor, which is why it can mask cancers. The masking effect is so pronounced that some studies estimate mammography's sensitivity drops from over 85 percent in fatty breasts to below 60 percent in extremely dense breasts. For women with dense tissue, a negative mammogram is far less reassuring than it is for other women.

Despite this, most screening guidelines in the United States do not mandate supplemental imaging for women with dense breasts. The U.S. Preventive Services Task Force, which sets the standard for many insurers, concluded in 2024 that there is insufficient evidence to recommend for or against supplemental ultrasound or MRI for women with dense breasts, citing a lack of randomized trials showing a reduction in breast cancer mortality. This stance leaves many women and their clinicians in a gray zone, unsure whether to pursue extra imaging.

The evidence that supplemental screening finds more cancers is clear, even if the mortality benefit is not yet proven. A large European study, the DENSE trial, published in New England Journal of Medicine in 2019, found that supplemental MRI for women with extremely dense breasts detected an additional 16.5 cancers per 1,000 women screened, compared with mammography alone. Ultrasound studies have shown similar, though smaller, incremental detection rates. These cancers are often small and node-negative, suggesting they are being caught at an earlier, more treatable stage.

Yet the uptake of supplemental screening remains low. A 2022 survey of breast imaging facilities in the United States found that fewer than one-third offered routine supplemental ultrasound to women with dense breasts, and even fewer offered MRI, which is typically reserved for women at very high lifetime risk. The reasons are multifaceted: cost, insurance coverage, patient anxiety, and the additional time required for these exams, which are more resource-intensive than a standard mammogram.

Patient awareness is another barrier. Although many states now require that women be notified of their breast density in their mammography report, a 2021 study in JAMA Network Open found that fewer than half of women who received such a notification understood what it meant or discussed it with their doctor. The notification, often phrased in clinical jargon, does little to empower patients to ask for supplemental imaging.

Evidence Suggests Supplemental Screening Works, Yet Uptake Lags

The evidence for supplemental screening is strongest for women at high risk, defined by family history, genetic mutations, or prior chest radiation. For these women, the American College of Radiology recommends annual MRI in addition to mammography, starting at age 30 or even earlier. MRI is more sensitive than ultrasound, detecting cancers that are invisible on both mammography and ultrasound, but it is also more expensive and less widely available, and it produces more false positives.

For women with dense breasts who are at average risk, the evidence is more nuanced. Ultrasound is the most accessible option, and it can be performed in the same setting as a mammogram, but it requires a trained sonographer and a radiologist to interpret the images in real time. The additional time and expertise translate into higher costs, which are not always covered by insurance. In a 2023 report from the American Cancer Society, researchers noted that while supplemental ultrasound could find an additional 2 to 3 cancers per 1,000 women, the false-positive rate was also higher, leading to more biopsies and more anxiety.

MRI is even more sensitive but also more expensive, with a single breast MRI costing several times more than a mammogram. It also requires intravenous contrast, which some patients cannot tolerate, and it is contraindicated in patients with certain metal implants or kidney disease. For these reasons, MRI is generally reserved for the highest-risk women, and even then, access is uneven. A 2024 study in Health Affairs found that Black and Hispanic women with dense breasts were significantly less likely to receive supplemental imaging than White women, even after controlling for insurance status.

The gap between evidence and practice is not simply a matter of cost. Radiologists cite workflow hurdles: adding supplemental ultrasound to a screening program means longer appointment times, more staff, and more complex scheduling. Reimbursement is also a challenge. Medicare and many private insurers have only recently begun to cover supplemental ultrasound for dense breasts, and coverage varies widely by state and plan. In some states, Medicaid does not cover it at all, leaving low-income women with the least access to the very imaging that could benefit them most.

Professional societies are divided. The American College of Radiology and the Society of Breast Imaging recommend that women with dense breasts be offered supplemental screening, but they stop short of a universal mandate. The U.S. Preventive Services Task Force, meanwhile, has called for more research on the mortality benefit, and it has not endorsed routine supplemental screening. This patchwork of guidance leaves individual clinicians to make their own decisions, often based on their personal experience and the resources available at their institution.

State Mandates and Professional Guidelines: A Patchwork

The lack of a federal standard for dense-breast care is striking. As of late 2024, more than 30 states have passed laws requiring that women be informed if they have dense breasts, but the laws vary in their details. Some require that the notification include a recommendation to discuss supplemental screening with a clinician, while others simply state the fact of density. A few states, including California and Texas, have gone further and mandated insurance coverage for supplemental ultrasound, but even these mandates have exceptions and limits.

At the federal level, the Food and Drug Administration (FDA) issued a rule in 2023 requiring that all mammography reports include a statement about breast density, but it stopped short of requiring that women be told what to do about it. The FDA's rule, which took effect in September 2024, also requires that reports indicate the level of density (heterogeneously dense or extremely dense) but does not mandate that clinicians recommend supplemental imaging. This leaves the decision to individual clinicians, who may or may not be aware of the latest evidence.

In Boston, the patchwork is visible in practice. Some hospital systems have adopted internal protocols that automatically refer women with dense breasts for supplemental ultrasound, while others leave it to the referring clinician's discretion. A 2023 audit of screening practices in Massachusetts found that the rate of supplemental ultrasound use varied by a factor of three across different facilities, even after adjusting for patient demographics. This variation suggests that where a woman lives, or which hospital she chooses, can determine whether she gets the extra imaging.

Insurance coverage is a major driver of this variation. Many private plans cover supplemental ultrasound for dense breasts, but some require prior authorization, and others charge a higher copay than for a standard mammogram. Medicare, which covers most women over 65, covers supplemental ultrasound for dense breasts as of 2023, but it requires that the woman have a clinical indication, such as a palpable lump or a high-risk profile. This means that a woman with dense breasts but no other risk factors may have to pay out of pocket, which can be a barrier for those with limited income.

The result is a system that is neither equitable nor evidence-based. Women who are well-informed, have good insurance, and live in a state with strong mandates are more likely to receive supplemental imaging. Others are left with a notification in their mammography report that they may not understand, and no clear next step. As one patient advocate in Boston put it, the density report is a start, but it is not a plan.

What Boston's Numbers Reveal About Trade-Offs

The falling recall rate in Boston is a double-edged sword. On one hand, it suggests that radiologists are becoming more accurate, and that AI tools are helping to reduce unnecessary callbacks. On the other hand, it may be contributing to an increase in interval cancers, particularly among women with dense breasts. A 2022 analysis of Massachusetts cancer registry data found that the interval cancer rate among women with dense breasts was nearly double that of women with non-dense breasts, and that this gap had widened over the past decade, even as overall recall rates declined.

Interval cancers are a key measure of screening effectiveness. They are cancers that are diagnosed in the interval between scheduled screenings, often because they were missed on the previous mammogram or because they grew rapidly. These cancers tend to be larger, higher grade, and more likely to be node-positive at diagnosis, all of which are associated with worse outcomes. A higher interval cancer rate is therefore a red flag that screening is not working as well as it should.

Radiologists face a difficult trade-off. If they lower their recall threshold, they will catch more cancers but also cause more false alarms. If they raise it, they will reduce false alarms but miss more cancers. The optimal threshold depends on the population being screened, and there is no one-size-fits-all answer. AI tools can help by identifying which findings are most likely to be cancer, but they are not yet sophisticated enough to account for breast density in a way that would change the threshold for individual women.

Quality metrics used by hospitals and insurers typically focus on recall rate and cancer detection rate, but they rarely include interval cancer rate. This is a missed opportunity. If interval cancer rate were tracked and reported, it might push facilities to adopt more nuanced screening protocols, such as offering supplemental ultrasound to women with dense breasts. Some researchers have called for a composite metric that combines recall rate, cancer detection rate, and interval cancer rate, to give a more complete picture of screening performance.

In Boston, some early adopters are already moving in this direction. At one academic medical center, radiologists have begun using a risk model that incorporates breast density, age, and family history to determine which women should be offered supplemental MRI, even if they are not at high lifetime risk. The program is still small, and the results are preliminary, but it represents a shift away from a one-size-fits-all approach to screening.

Closing the Gap: Practical Steps and Their Limits

Several concrete steps could narrow the gap between evidence and practice. At the clinic level, the first step is to adopt standardized density reporting across all facilities, using the same categories and language. This would reduce confusion and make it easier to track outcomes. The second step is to implement shared decision-making for supplemental imaging, where clinicians discuss the risks and benefits with each woman, taking into account her density, risk factors, and preferences. This is not a one-time conversation but an ongoing dialogue that should be revisited as new evidence emerges.

Risk models can help target supplemental screening to those who need it most. Several validated models, such as the Tyrer-Cuzick model and the Breast Cancer Surveillance Consortium risk model, incorporate breast density along with other factors to estimate a woman's risk of developing breast cancer. Using these models to guide who gets supplemental MRI or ultrasound could improve the efficiency of screening while reducing unnecessary exams. However, these models are not perfect, and they require data that may not be readily available in all practices.

Advocacy for insurance coverage is also critical. While some states have mandated coverage for supplemental ultrasound, many have not, and even where coverage exists, it may not extend to MRI. Patients and clinicians can push for broader coverage by documenting the benefits of supplemental screening and by raising awareness of the disparities in access. A 2024 report from the National Cancer Institute highlighted that women with dense breasts who receive supplemental MRI have a lower incidence of interval cancer, but the report also noted that MRI is underused, particularly among minority populations.

Patient education is the foundation. Women need to understand what breast density means, what their own density is, and what their options are. This is not about alarming women but about empowering them to make informed decisions with their clinicians. A simple conversation after a mammogram, prompted by the density notification, can go a long way. As one Boston radiologist said, the density report is a starting point, but it should not be the end of the conversation.

Yet these steps face real limitations. Supplemental screening is not cheap, and the added costs could strain already stretched healthcare budgets. Overdiagnosis is a genuine concern: some cancers detected by MRI or ultrasound may never have caused symptoms or threatened a woman's life, leading to unnecessary treatment and anxiety. The false-positive rate of supplemental imaging is higher than that of mammography alone, which means more biopsies and more worry for many women. Moreover, the infrastructure required for widespread MRI screening—machines, radiologists, and scheduling—is not available in many communities, particularly rural areas. The evidence for mortality benefit is still incomplete, and until randomized trials report results, some clinicians may remain skeptical. Finally, the burden of additional imaging may fall disproportionately on women who can afford it, widening existing disparities rather than closing them.

These trade-offs do not negate the potential benefits, but they underscore the need for a measured approach. The falling recall rate in Boston should be celebrated, but not at the expense of the women who are being left behind. As the evidence evolves, so too should the protocols that determine who gets screened, and how.

This article is for informational purposes only and is not a substitute for professional medical advice. Always discuss your individual risk and screening options with your healthcare provider.