Mammogram vs. Breast MRI

A mammogram is the standard test for breast cancer screening. Sometimes it can be used together with breast magnetic resonance imaging (MRI) to detect or rule out breast cancer for women at high risk of the disease.

Breast MRIs can detect tumors that mammograms may miss, but they also have the potential to mistakenly identify non-cancerous breast tissue as cancer, which can lead to a false-positive result.

Usually, breast MRIs are expensive, and the cost isn't always covered by health insurance. The question of when a breast MRI is appropriate hinges on whether it can deliver a high degree of reliability without causing extra worry and cost.

A newer screening tool called fast breast MRI or abbreviated MRI may help bridge some of these gaps.

This article will outline the mammogram and MRI's different purposes, indications, advantages, and limitations.

Procedures

During a mammogram, X-ray radiation is used to penetrate breast tissue and record differences in tissue density. Solid tumors will typically have a higher density than normal tissue and will show up on an X-ray as a lighter, solidified mass.

Different views of the breast are taken to comprehensively visualize all areas of breast tissue. To obtain the best image, the breast is compressed to allow radiation to penetrate thinner layers of tissue.

With an MRI, compression is not needed. During this test, you would be placed in a tube-like machine that emits powerful magnetic and radiation waves to generate highly detailed cross-sectional images of the breast.

To differentiate tissue density, a contrast dye, usually gadolinium, is injected to enhance the image resolution by 10- to 100-fold compared to a mammogram. The gadolinium is naturally cleared from the body in the urine.

Test Sensitivity

Test sensitivity describes the ability of a test to identify a disease without missing evidence of the disease. Sensitivity is the term used to describe the percentage of time a test makes a correct positive diagnosis.

The sensitivity of a mammogram for identifying breast cancer differs based on whether a woman has dense breasts, while the sensitivity of a breast MRI is more consistent.

Comparing breast cancer sensitivity of mammogram and breast MRI:

• Generally speaking, a mammogram has an average sensitivity of around 87%.
• In women with dense breasts (seen on a mammogram as areas of opacity and striation), the sensitivity of a mammogram can drop between 48% to 64%, according to a 2015 review of studies in the American Journal of Roentgenology.
• Because MRI offers a higher resolution, it is better able to provide images of masses in dense tissue. A breast MRI has a sensitivity ranging from 81% to 100% in women with different risk profiles.

False Positives

Specificity in breast cancer diagnosis is the ability of a test to avoid misidentifying normal tissue as breast cancer. Specificity is the percentage of times a test correctly yields a negative result.

Despite its imaging capabilities, breast MRIs are notoriously variable when it comes to specificity—they are prone to false-positive results. The main reason for this is that an MRI will enhance both benign and cancerous lesions, often with little differentiation in their characteristics.

A mammogram can detect calcification (the characteristic deposit of calcium around a malignancy) that can help differentiate benign (non-cancerous) from malignant (cancerous) tumors.

Comparing breast cancer specificity of mammogram and breast MRI:

• According to the current body of evidence, the specificity of breast MRI can range from as high as 97% to as low as 37%.
• A mammogram has approximately 89% specificity for breast cancer.

Possible Risks

Women may worry that exposure to radiation during a mammogram can place them at risk of developing cancer. Most of the current evidence suggests that the risk of this is low, even with annual mammogram screening.

According to a 2016 study in the Annals of Internal Medicine, around 125 of every 100,000 women who undergo an annual mammogram will develop radiation-induced breast cancer (0.00125%). Of those, 16 (0.00016%) will die.

There has also been an ongoing debate as to whether gadolinium used in MRI poses a health risk. The concerns first arose in 2014 when a study reported that the contrast dye could be retained and deposited in the brain. Most current research suggests that this is not harmful.

Despite this, the U.S. Food and Drug Administration issued a safety announcement in 2017, recommending that patients be advised about gadolinium retention prior to undergoing an MRI.

Costs

Any health screening tool must fulfill three criteria to be effective in a public health setting: reliability, availability, and affordability. By and large, a mammogram fulfills these aims.

From a cost perspective, a mammogram is relatively affordable, ranging from $75 to $250, depending on the facility and where you live. A breast MRI with contrast dye may cost you anywhere from $750 to $2,500 or more.

While newer rapid breast MRI tests are becoming more affordable, many insurance companies will not cover a breast MRI of any sort unless an abnormality is found.

According to a 2019 study in Cancer, routine mammogram screenings reduce the risk of breast cancer by at least 60% over 10 years.

When to Have a Breast MRI

Women who are at high risk for developing breast cancer should have a discussion with their healthcare providers about whether having a breast MRI in addition to a standard mammogram would be beneficial.

High-risk individuals include those who:

• Have the genetic mutations BRCA1 and BRCA2
• Have one of the other genetic mutations associated with breast cancer, such as CHEK2, PALB2, ATM, and others
• Have a first-degree relative with a familial breast cancer mutation
• Had radiation therapy to the breast between the ages of 10 and 30, such as to treat Hodgkin lymphoma
• Have a lifetime breast cancer risk of 20% to 25% based on assessment tools issued by the National Cancer Institute

Women who have had breast cancer or conditions that predispose them to the disease (such as atypical ductal hyperplasia) may also need an MRI. Women who have had a mastectomy on one side are often offered regular MRIs on the contralateral (non-involved) breast. Those with dense breasts on a mammogram may also need a breast MRI.

Conventional vs. Fast Breast MRI

Women who have dense breasts are at an increased risk of developing breast cancer, and dense breasts make mammograms less sensitive. In some states, women who are found to have dense breasts on mammography are now required to be informed of the diagnosis and may wish to undergo additional testing.

Combining mammography and breast ultrasound has been found to improve detection to some degree, but with an increased risk of false positives.

A newer MRI technique referred to as fast breast MRI or abbreviated MRI may be combined with mammography in this situation. Unlike conventional MRI, a fast MRI takes only around 10 minutes, and unlike the high cost of conventional MRI, fast MRI costs roughly the same as a mammogram.

In studies thus far, the combination of mammography with fast MRI detected significantly more breast cancers than mammography alone (or combined with ultrasound), especially aggressive breast cancers. Since the technique is relatively new, it is not yet available at all breast cancer screening centers.

Summary

A mammogram is the standard test for breast cancer screening. For women who are at increased risk, breast MRI is increasingly used to help in the diagnosis. Although MRIs can detect tumors that mammograms sometimes miss, they run the risk of showing a false-positive result. However, when both are used together, they can help diagnose breast cancer.

A Word From Verywell

Recommendations for when to do an MRI for breast cancer screening are relatively new. The same applies to identifying the genetic mutations that can place you at risk. There are a number of genetic tests today that can detect 15 key mutations associated with breast cancer.

You can work with your healthcare provider and a genetic counselor to have a clearer picture of your screening needs.

Please note that at-home screening tests are not adequate to screen for a genetic predisposition to breast cancer because they don't test for most BRCA mutations.

For women at risk of breast cancer, groups such as FORCE (Facing Our Risk of Cancer Empowered) can provide helpful updated information and connection with others facing similar concerns.