James Metz, MD and Carolyn Vachani, RN, MSN, AOCN
Abramson Cancer Center of the University of Pennsylvania
Last Modified: June 18, 2009
A mammogram is a low dose x-ray used to detect breast cancer and other abnormalities in breast tissue. Mammograms have been used since the late 1960s, but the technology has advanced greatly over time. A screening mammogram is done in a woman with no symptoms of breast cancer. If the mammogram is being done because a lump or abnormality was detected during an exam, it is called a diagnostic mammogram.
The screening mammogram consists of a two-view exam of each breast, one "picture" taken looking from top-to-bottom (craniocaudal) and one looking side-to-side (mediolateral oblique). These "pictures" or films are then compared to the patient's previous films to look for changes or abnormalities that need further investigation.
The diagnostic mammogram is done to further define the location or characteristics of an abnormality detected during a screening mammogram. It is also performed in patients who have a suspicious lump on physical exam or patients that have had breast cancer in the past that was treated with breast conservation techniques. Patients who have had breast augmentation (enlargement) also require diagnostic mammograms with specialized views of the breast. Special techniques, such as exaggerated oblique projections, spot compressions, and magnified spot views, are utilized in diagnostic mammograms.
The mammogram pictures are then "read" by a radiologist, whose job it is to interpret what the picture shows. When "reading" the mammogram films, the radiologist looks for specific findings considered suspicious for malignancy. Microcalcifications that are pleomorphic, 5 or more in number, and/or in linear or clustered patterns are considered worrisome. Masses that are spiculated, stellate, or associated with microcalcifications are also considered suspicious. The radiologist also looks for any new abnormalities compared to previous mammograms. It is important that the patient has mammograms performed at the same institution each time, or brings mammograms that were previously done for comparison purposes.
In the last 15 years, digital mammogram has become more common. This technology takes a similar image to film mammography, but uses digital technology. This allows for digital storage and transfer of images, higher resolution , images can be manipulated to enhance visualization of abnormalities, and less waiting time for the patient, since films do not need to be developed. The main disadvantage to digital machines is the cost, which can be up to four times as much as a standard film machine. Many assumed this technology would lead to improved diagnosis, but it is an example of why clinical studies are so important. The Digital Mammographic Imaging Screening Trial enrolled almost 50,000 women and compared film mammography to digital. The study found that for most women there was no difference in detecting breast cancer. There were a few groups that did have superior detection with digital technology - young, premenopausal and perimenopausal women and those with dense breast tissue.
Studies over the past 30 years have shown that mammograms offer a benefit to women over age 40 in finding breast cancers at their earliest stages, when they are most curable. There is no defined age to stop having mammograms, and this should be determined based on a woman's health and other medical conditions.
Mammograms are the best tool we have to detect cancers early; however, they are not perfect. About 20-30% of breast cancers are not detectable with mammogram (called "mammographically occult") or are missed due to dense breast tissue or other factors. If a woman or her healthcare provider detect a lump, but nothing is found on a mammogram, further testing is warranted. This is called a false negative; the test is negative for an abnormality, but there is actually one present. On the other hand, there is the chance of a false positive, which is when a mammogram is read as having an abnormality, but no cancer is present. The downside to this is that an abnormal mammogram requires follow up with additional tests (ultrasound, repeat mammogram) or biopsy. This can cause considerable anxiety for the woman. It is important to note that about 10% of women having a mammogram will be called back for additional films or ultrasound to clarify a finding. Of those, about 10% will need to have a biopsy and about 75% of breast biopsies will turn out to be benign (not cancer).
With its faults, mammogram is still the most reliable test we have to detect breast cancer early when it is most curable. Other tests, such as ultrasound and MRI, have been studied and do not provide the levels of accuracy seen with mammogram for the general population. Learn more about MRI screening for breast cancer. Tomotherapy, scintimammography and contrast enhanced mammography are some of the new technologies being explored in breast cancer screening.
The current American Cancer Society Screening Recommendations are for women age 40 and older to have a mammogram every year and to continue to do so as long as they are in good health. Women in their 20s and 30s should have a breast exam by their healthcare provider at least every 3 years and yearly after age 40. Breast self-exam is a good idea for women beginning in their 20s. This will allow the woman to have a good understanding of their normal breast tissue and be better able to detect a change.
Read more about Breast Imaging Data Reporting System (BI-RADS®), which was developed by the American College of Radiology as a way to standardize mammography reporting by radiologists.