An MRI can help doctors look beyond what a mammogram reveals, especially for women with a high risk of breast cancer.
Mammograms are an effective breast cancer screening for women who have a low or average risk for the disease. But in many cases, mammograms alone may not be sufficient. If more testing is needed, or if a woman is at higher risk for breast cancer, a doctor may order an MRI, or magnetic resonance imaging, to supplement a mammogram.
When do doctors order a secondary MRI?
A doctor will ask his or her patient to undergo an MRI if the patient has specific risk factors. These criteria can be grouped into two categories—hereditary gene mutation and family history of breast cancer. Women who meet either or both of these criteria may need to supplement a mammogram with an MRI:
- Hereditary gene mutation—According to the American Cancer Society, only 5 to 10% of breast cancer cases are hereditary¹. Hereditary breast cancer is caused by mutations that are passed directly from a parent. The most common inherited gene mutations are BRCA1 and BRCA2. Woman who have these gene mutations may require an MRI for their doctor to be able to diagnose and stage their condition. Women with a BRCA1 or BRCA2 gene mutation have a 70% chance of developing breast cancer before age 80.
- A family history of breast cancer—Family history plays an extremely important role in determining how likely a woman is to develop breast cancer. And not all family members affect breast cancer the same way. For example, women with one "first-degree relative" (a mother, a sister, or a daughter) who have had breast cancer are twice as likely to get the disease; women with two first-degree relatives are five times likelier². Women with other family members who have had breast cancer, such as an aunt or a cousin or a male relative, are also likelier to develop breast cancer.
What can an MRI detect?
An MRI, unlike an X-ray or a CT scan, does not use radiation. Rather, it creates a magnetic field that realigns the hydrogen atoms in a patient's body. The MRI generates images of the inside of the body in slices, almost like a loaf of bread. Depending on the type of equipment used, and the particular kind of images a doctor has ordered, the MRI machine can render 3D cross-sections of body tissue that allow for close analysis.
The process of getting an MRI is more invasive than a mammogram, as it often requires the use of a contrast dye, which is injected through the patient's arm, and can cause some discomfort. Doctors order MRIs for patients to differentiate between layers of tissue, and more clearly see areas of concern that a mammogram might miss.
How should patients prepare for an MRI?
The MRI facility will provide detailed instructions on how to prepare. Leading up to the test, patients receive a consultation from the technician and written instructions that highlight important dos and don'ts. For example, pregnant women should not get an MRI as a precaution³. The test takes places in an enclosed cylinder, so patients who have anxiety or claustrophobia can be prescribed a medication to help with feelings of unease.
Patients are instructed to disclose anything that might alter the results of the MRI. For example, tattoos that have especially dark ink, and medical prostheses, such as a pacemaker or an artificial limb.
What can patients expect during the test?
An MRI machine is quite large. Patients being screened for breast cancer lie face down on a table. The table slides into a long, narrow tube, where the actual test takes place. Before the test, patients remove anything metal, such as jewelry or piercings. The process itself is painless, and can last anywhere from 15 minutes to an hour. Because the machine generates quite a bit of noise during the test, patients may use earplugs or request music³. The patient can communicate with the MRI technician at any time via a microphone.
After the test, the patient can resume normal activities. If the patient took a sedative or anti-anxiety medication, the MRI facility may insist that a friend or family member drive the patient home.
What happens next?
The patient's doctor will review the results of the MRI and go over them with the patient. Depending on what he or she sees, the doctor may order additional testing, or prescribe a course of treatment—next steps depend on what the MRI reveals.
- Breast Cancer Risk Factors You Cannot Change. https://www.cancer.org/cancer/breast-cancer/risk-and-prevention/breast-cancer-risk-factors-you-cannot-change.html. Accessed June 23, 2018.
- Breast Cancer Risk Factors: Family History. https://www.breastcancer.org/risk/factors/family_history. Accessed June 25, 2018.
- MRI - Mayo Clinic. https://www.mayoclinic.org/tests-procedures/mri/about/pac-20384768. Accessed June 25, 2018.