Getting regular mammograms is one of the best things you can do for breast health. For most women, these low-dose X-rays of the breast are the best way to detect breast cancer in the earliest stages, when treatment is most likely to be successful. This type of mammogram, called a screening mammogram, can often identify breast lumps years before they can be felt.
But mammograms aren’t just screening tools. There is a second primary type of mammogram — a diagnostic mammogram — that doctors order if the results of a screening mammogram are suspicious or if you’re experiencing signs and symptoms of breast cancer. Read on to learn more about screening vs. diagnostic mammograms: their similarities, differences, and when and why they’re performed.
A screening mammogram detects changes in the breast tissue that that could be indicative of breast cancer in women who have no signs or symptoms of the disease. The value of getting regular screening mammograms cannot be understated: They have helped reduce deaths from breast cancer by 43 percent since 1989. While some people with breast cancer experience symptoms of the disease—most commonly a new lump or mass—mammograms can detect the disease significantly sooner, sometimes up to three years before you or your doctors can feel a mass.
Considering that certain types of breast cancer, such as triple-negative breast cancer and inflammatory breast cancer, can grow and spread rapidly, early detection and prompt treatment are critical to successful outcomes.
There are five main types of changes doctors look for during a screening mammogram:
Calcifications: These are deposits of calcium in the breast tissue that appear as white dots on a mammogram. They may be tiny specks, called microcalcifications, or larger (macrocalcifications). The presence of calcifications is not always a sign for alarm: Most macrocalcifications simply occur with aging, and they can also result from inflammation, infection, or prior injury to the breast. Microcalcifications can also be benign, but they are more likely to be caused by cancer than macrocalcifications. Thirty to 50 percent of breast cancers that cannot be felt are identified solely by microcalcifications on a mammogram.
Masses: A mass is an area of abnormal breast tissue with a shape and edges that don’t resemble the rest of the tissue in the breast on a mammogram. Masses can be a sign of breast cancer, especially those that are solid, but even most solid masses are benign. It’s more common for a mass to be a non-cancerous issue such as a fibroadenomas or a simple cyst (fluid-filled sac).
Asymmetries: Breast asymmetry means that one breast (or portion of the breast) is different from the other in size, volume, form, or position. It’s a common finding that is usually benign, with causes ranging from hormonal changes to injury to the breast. But if there is a large variation in asymmetry, it may indicate breast cancer.
Architectural distortions: This term describes areas of breast tissue that appear to be pulled or distorted toward a certain point. They are not necessarily cause for alarm, since they may be due to past injury or a procedure performed on the breast. And some asymmetries result simply from the way the breast was positioned during a mammogram.
Breast density: A mammogram also measures breast density, or the amount of much fibrous and glandular tissue you have in your breasts compared to fatty tissue. There are four categories of breast density that range from A (mostly fatty tissue) to D (extremely dense). While it’s perfectly normal to have dense breasts—about half of all women do and women’s breasts tend to be denser when they’re younger—it is associated with a slightly higher risk of breast cancer. It’s not clear why this association exists, but it may be that there are more cells present in dense breast tissue that can become abnormal. To complicate matters, it’s more difficult for a radiologist to see cancer on your mammogram if you have dense breasts. Talk to your doctor about whether you should consider getting additional tests, such as breast ultrasound and/or magnetic resonance imaging (MRI), if your doctor hasn’t already recommended them.
For women at average risk of breast cancer, most major health organizations recommend starting screening mammograms at age 40. However, those at high risk of developing the disease should begin screening earlier. Women at high risk are those who:
If you’re wondering when you should start screening mammograms, ask your doctor to perform a breast cancer risk assessment.
How often should you get a screening mammogram? Again, recommendations vary among health organizations—some say annually, others biannually depending on age. You and your doctor will discuss the ideal frequency for you based on factors such as your family history of breast cancer, genetics, and so on.
A diagnostic mammogram provides a more detailed image than a screening mammogram and is used to evaluate abnormalities in the breast. Your doctor may order a diagnostic mammogram if he or she observes something unusual on your screening mammogram (such as one of the findings mentioned above) or if you’re experiencing signs and symptoms that may indicate breast cancer. These include:
It’s natural to feel anxious if your doctor orders a diagnostic mammogram, but keep in mind that the findings are more likely to be benign than malignant. Also, there are also some special circumstances when a diagnostic mammogram is recommended that have nothing to do with suspicious areas on a screening mammogram or symptoms that could indicate breast cancer.
For example, diagnostic screening is ordered for women with breast implants. The presence of implants, whether they contain saline or silicone, makes it difficult for see all your breast tissue on a screening mammogram, whereas a diagnostic mammogram can better detect any abnormalities that may be obscured by the implants. In addition, you may be called back for a diagnostic mammogram following a screening mammogram if the images were blurry or they didn’t capture all of your breast tissue.
A screening mammogram and a diagnostic mammogram are similar in many ways: The same machine is used, your breasts are compressed with clear plastic paddles before the images are taken, and the steps you need to take to prepare for both tests (such as not wearing deodorant, lotion, or perfume on your breasts or under your arms, etc.) are the same.
So what is the difference between a diagnostic mammogram vs. a screening mammogram? There are three main things that set them apart:
The number of images taken: Two or more images of each breast are captured during a screening mammogram, usually from top to bottom and side to side. During a diagnostic mammogram, the technologist takes more images that provide radiologists with a detailed view of the breast from several different angles. He or she may also use different imaging techniques, which can include magnification and spot compression, to get a closer look at the area(s) of concern. As a result, it takes longer for technologists to perform diagnostic mammograms than screening mammograms, which are usually completed in about 20 minutes.
The dose of radiation: Since more images are captured, you receive a higher dose of radiation during a diagnostic mammogram than during a screening mammogram. But the dose is still very small, and experts agree that the benefits of getting mammograms outweigh any negative effects of radiation exposure. If you’re concerned about potential risks involved, speak with your doctor.
When the radiologist interprets the results: When you get a screening mammogram, it takes several days for a radiologist to evaluate the images and report the findings to your doctor. But during a diagnostic mammogram, the radiologist typically evaluates the X-rays while you’re at the testing facility in case he or she needs to request additional images. Based on the results, your doctor may recommend additional types of tests, such as an ultrasound of the breast.
Read about additional modalities for breast cancer screening—and how BCRF researchers and other investigators are working to improve mammography—here.
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