What is a Mammogram?
Last updated: October 2021
Mammography is the use of x-rays to take pictures of the breast tissue. During a mammogram, the breast is compressed between two plates to evenly spread out the tissue for a clearer image. Mammograms are an imperfect tool, as they may not find every breast cancer or may find lumps that turn out to not be cancerous, but they are currently the best screening tool available.
Screening mammograms are used in women who are not having any symptoms of breast cancer. The goal of screening mammograms is to detect potential cancers that are in their earliest (and most treatable) stages.1
Screening mammograms usually involve two images of each breast. The breast is placed between a specific platform and a plastic plate, then compressed to evenly distribute the breast tissue and hold the breast still for the x-ray image. One image is taken from a top-to-bottom view, and one image is taken from an angled side view.2
Recommendations for screening mammography can vary. However, in women of average risk for breast cancer, screening mammograms are generally begun no later than age 50. Most guidelines recommend yearly or biennial (every other year) mammograms between the ages of 50 and 74 for women at average risk of breast cancer. However, some organizations recommend screening mammography begin for women in their 40’s. For women at a higher risk for breast cancer, such as those with a personal or family history of breast cancer, or those who have a known genetic mutation (like BRCA), screening mammograms may be started at younger age and/or recommended more frequently.3
Diagnostic mammograms are used when someone is having a symptom that may be indicative of breast cancer, such as a lump, changes in the skin of the breast, nipple discharge, or change in the size or shape of a breast. Diagnostic mammograms may also be used if an abnormality was detected in a screening mammogram.1
The same mammography machine used in screening mammograms is also used for a diagnostic mammogram. During a diagnostic mammogram, additional views are taken of the breast.1
Risks of mammography
Since mammograms are x-rays, there is some exposure to radiation. However, the amount of radiation used for mammograms is typically small and the benefit of finding cancers early generally outweighs the risk.2
Mammograms can cause false positives, when test results show something (such as a suspicious, possibly cancerous area on a mammogram) that is actually not concerning. False positives occur more frequently in younger women or women with dense breast tissue, and can require women to undergo additional testing, including ultrasound and biopsies.4
Limitations of mammography
Mammograms cannot tell with certainty the difference between a cancerous spot and a benign (non-cancerous) one, and additional tests may be needed for a suspicious area. Additional tests may include ultrasound and/or a biopsy.
Mammograms are not perfect and may not detect all breast cancers. In addition, cancers can be more difficult to detect on mammograms in women who have dense breast tissue. Breast implants may also make detecting breast cancers in mammograms more challenging, as the breast implant can potentially hide some breast tissue (it is important for patients to alert their mammogram professional if they have breast implants as certain mammogram techniques can help to account for this).1,2
What if a mammogram is abnormal?
If a screening mammogram finds an abnormality or suspicious area, additional mammograms, ultrasound, and/or a biopsy may be required. An abnormal finding on a mammogram does not necessarily mean that it is cancer, as many other benign (non-cancerous) conditions may cause abnormalities to appear on a mammogram. Additional tests can help determine the cause and what next steps need to be taken.5