Mammography is the primary screening tool used to test for breast cancer. Current guidelines recommend that women at average risk begin screening mammograms at age 40 and continue every two years through age 74. Depending on your risk level and breast density, additional imaging like 3D mammography, ultrasound, or MRI may also play a role.
Mammography: The Standard Screening Tool
A screening mammogram is a low-dose X-ray of the breast designed to detect cancer before you can feel a lump or notice any symptoms. During the exam, a technologist captures two views of each breast. The entire process is quick, though the compression can be uncomfortable for a few seconds per image.
Mammography remains the only screening method proven to reduce breast cancer deaths at a population level. Modeling data from the U.S. Preventive Services Task Force estimates that screening every two years from age 40 to 74 averts about 8.2 breast cancer deaths per 1,000 women over a lifetime, compared to 6.7 deaths averted when screening starts at 50. For Black women, who face higher rates of aggressive breast cancers at younger ages, starting at 40 averts roughly 10.7 deaths per 1,000 women versus 9.2 when starting at 50.
Screening vs. Diagnostic Mammograms
A screening mammogram is what you get when you have no symptoms and are simply checking in on schedule. If something suspicious shows up on that screening, or if you have symptoms like a lump, nipple discharge, or breast pain, you’ll be called back for a diagnostic mammogram. The diagnostic version focuses on the area of concern with additional or magnified views, and a radiologist typically reviews the images while you’re still there so follow-up decisions can be made the same day.
3D Mammography (Tomosynthesis)
Many screening centers now offer 3D mammography, also called digital breast tomosynthesis, which takes multiple thin-slice images of the breast and reconstructs them into a three-dimensional picture. This makes it easier to distinguish between overlapping tissue and an actual mass, which is especially helpful for women with denser breasts.
Compared to standard 2D digital mammography, 3D mammography detects more cancers: studies in women with a family history of breast cancer found detection rates of 5.1 to 11.6 cancers per 1,000 screens with 3D, versus 3.8 to 8.3 per 1,000 with 2D. Just as important, 3D mammography tends to reduce false alarms. Recall rates (being called back for additional imaging after a screening) ranged from 2.7% to 4.5% with 3D, compared to 2.8% to 11.5% with 2D. Three out of four studies found that 3D had lower callback rates.
Breast MRI for High-Risk Women
If your estimated lifetime risk of breast cancer is 20% or higher, guidelines from the American College of Radiology recommend adding annual breast MRI to your screening routine. MRI uses magnetic fields rather than radiation to produce detailed images and is particularly good at catching cancers that mammography might miss in dense or high-risk tissue.
A lifetime risk of 20% or more can come from strong family history or from carrying certain genetic mutations. The mutations that carry the highest risk include BRCA1 and BRCA2 (over 60% lifetime risk) and TP53 (also over 60%). Several other mutations, including PALB2 and CDH1, carry a 41% to 60% lifetime risk. Others like ATM, CHEK2, and RAD51C fall in the 20% to 40% range. Women who carry these mutations, or untested first-degree relatives of carriers, are generally advised to start annual MRI between ages 25 and 30, years before routine mammography screening would begin.
MRI is not used for average-risk screening because it produces more false positives and is significantly more expensive than mammography.
Ultrasound and Dense Breast Tissue
Breast density is scored on a four-level scale, and roughly half of women over 40 have dense breast tissue. Dense tissue appears white on a mammogram, just like tumors do, which can make cancers harder to spot. You’ll be notified of your breast density category after every mammogram, as all 50 U.S. states now require this disclosure.
Ultrasound is sometimes offered as a supplemental screening tool for women with dense breasts. It can find small cancers hidden by dense tissue. However, the American College of Obstetricians and Gynecologists does not recommend routine supplemental screening (ultrasound, MRI, or other tests) for women who have dense breasts but no additional risk factors, because current evidence hasn’t shown that these extra tests reduce breast cancer deaths in that group. If you have dense breasts plus other risk factors, such as a family history or a known genetic mutation, the calculus shifts and supplemental imaging is more likely to be recommended.
What Your Results Mean: BI-RADS Scores
Every breast imaging report assigns a standardized score from 0 to 6, known as a BI-RADS category. Understanding these numbers can take some of the anxiety out of waiting for results.
- Category 0: The images were incomplete or unclear, and you’ll need additional views or a different type of imaging before the radiologist can give a final reading.
- Category 1: Negative. No cancer detected.
- Category 2: Also negative, though some benign findings like simple cysts may be noted. Routine screening continues on your normal schedule.
- Category 3: Probably benign, with roughly a 2% chance of cancer. A follow-up scan in six months is typically recommended to confirm nothing has changed.
- Category 4: A suspicious finding that warrants a biopsy. This category is subdivided: 4A means a 2% to 10% chance of cancer, 4B means 10% to 50%, and 4C means 50% to 95%.
- Category 5: Highly suggestive of cancer, with a 95% likelihood. A biopsy is strongly recommended.
- Category 6: Reserved for women who already have a confirmed cancer diagnosis. Images in this category track how the cancer responds to treatment.
Getting called back after a screening mammogram is common and does not mean you have cancer. Most callbacks result in additional imaging that turns out to be benign.
How Screening Guidelines Differ
The two most widely referenced sets of guidelines in the U.S. don’t fully agree, which can be confusing. The USPSTF recommends mammograms every two years starting at age 40 through age 74 for all women at average risk. The American Cancer Society takes a slightly different approach: women ages 45 to 54 should get mammograms every year, women 55 and older can switch to every two years, and women ages 40 to 44 have the option to start annual screening if they choose. The ACS recommends continuing screening as long as a woman is in good health and expected to live at least 10 more years.
Neither organization recommends clinical breast exams (physical exams performed by a healthcare provider) as part of routine screening for average-risk women. Self-awareness of how your breasts normally look and feel remains useful for noticing changes, but structured self-exams are no longer a formal recommendation from most major guidelines.