30-Second Summary
A mammogram is a low-dose X-ray of the breast; screening mammograms can find tumors before they cause symptoms.
Mammograms can show masses, calcifications, and breast density; a radiologist looks for unusual changes.
Results are reported using BI-RADS categories (0–6), each with a recommended follow-up.
The USPSTF recommends women at average risk get screening mammograms every 2 years from ages 40 to 74.
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The simple version
A mammogram is an X-ray image of the breast. Screening mammograms are used to look for breast cancer because they can find tumors at an earlier stage, before they cause symptoms. The same machine can also take a diagnostic mammogram — used to check a lump or other change after it's found, with images from more angles.
What a mammogram can show
A radiologist studies the images for unusual changes, comparing them with your past mammograms when possible. Mammograms can show:
- A mass (breast lump). Its size, shape, and edges matter. A smooth, round lump with clear edges is often a benign cyst; a jagged outline or irregular shape may need more tests.
- Calcifications — tiny calcium deposits, not related to calcium in your diet. Larger ones (macrocalcifications) are usually benign; tiny ones grouped together (microcalcifications) can sometimes signal DCIS or breast cancer.
- Breast density — the mix of dense and fatty tissue. Mammography is more likely to miss cancer in dense breasts.
What to expect
During the exam, your breast is placed between two plates that press together to produce a clearer picture. Several images are taken from different angles. The compression can be uncomfortable or briefly painful; an over-the-counter pain reliever beforehand may help, and it's best not to schedule the test right before or during your period. Avoid deodorant, powder, lotion, or perfume on the breasts and underarms that day.
How results are reported (BI-RADS)
You'll usually get the radiologist's report within about two weeks. It typically includes a BI-RADS category — a standard way of describing findings and the recommended follow-up:
- 0 — More imaging needed before a category can be assigned
- 1 — Negative; continue regular screening
- 2 — Benign finding; continue regular screening
- 3 — Probably benign; a 6-month follow-up mammogram
- 4 — Suspicious; may require a biopsy
- 5 — Highly suggestive of cancer; requires a biopsy
- 6 — Known, biopsy-proven cancer
Being called back for more testing can feel scary, but most people who are called back are not found to have breast cancer.
When to be screened
The U.S. Preventive Services Task Force recommends that women at average risk have screening mammograms every 2 years between ages 40 and 74. People at higher risk — for example, those with harmful BRCA1 or BRCA2 gene changes, or who received chest radiation for a childhood cancer — may be advised to begin earlier or screen more often. Your doctor can help you understand your own risk based on your personal and family history.
Cost and access
Mammograms are available at breast clinics, hospital radiology departments, mobile vans, and radiology and doctors' offices, and you may be able to schedule a screening mammogram without a referral. Under the Affordable Care Act, screening mammograms are covered as a preventive benefit every 1–2 years for women 40 and over without copays; Medicare covers annual screening mammograms for beneficiaries 40 and older. For uninsured or low-income individuals, the CDC's National Breast and Cervical Cancer Early Detection Program offers free or low-cost screening, and NCI's Cancer Information Service (1-800-4-CANCER) can help you find a certified facility.
Words to know
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Common questions
▸What is a mammogram?
Mammograms are X-ray images of the breasts. They are used for breast cancer screening because they can find tumors at an earlier stage, before they cause symptoms. A mammogram can also be used to check for cancer after a lump or other change is found — this is called a diagnostic mammogram.
▸What can a mammogram show?
Mammograms can show a mass (breast lump), deposits of calcium called calcifications, breast density, and other changes. A radiologist studies the images for unusual changes and, when possible, compares them with your past mammograms. A smooth, round lump with clear edges is often a benign cyst, while a jagged or irregular shape may need more tests.
▸What happens during a mammogram?
Your breast is placed between two plates that press together, which helps produce a clearer X-ray. Several images are taken from different angles. The compression can be uncomfortable or briefly painful for some people; an over-the-counter pain reliever beforehand may help. Try not to schedule it right before or during your period, and avoid deodorant, powder, or lotion on the breasts and underarms that day.
▸What do BI-RADS categories mean?
BI-RADS is a standard way radiologists report mammogram findings, from 0 to 6, each with a recommended follow-up. For example, category 1 is negative and category 2 is a benign finding — both mean continue regular screening; category 0 means more imaging is needed; and categories 4 and 5 (suspicious or highly suggestive of cancer) may require a biopsy. Your results letter explains any follow-up you need.
▸When should I have a screening mammogram?
The U.S. Preventive Services Task Force recommends that women at average risk have screening mammograms every 2 years between ages 40 and 74. People at higher risk — such as those with harmful BRCA1 or BRCA2 gene changes, or who had chest radiation for a childhood cancer — may be advised to start earlier or screen more often. Talk with your doctor about your personal risk.
▸What is a 3D mammogram?
Three-dimensional mammography, also called digital breast tomosynthesis (DBT), takes pictures of thin 'slices' across the breast that are assembled into a 3D image. DBT combined with standard mammography is better at finding tumors than standard mammography alone, though it is not yet known whether it reduces deaths from breast cancer more effectively. An NCI-sponsored trial is studying this question.
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