Mammography, the primary means of screening women at average risk for breast cancer, involves X‑ray radiation passing through the breast, producing an image on film or on a digital recording plate. It utilizes a low dose of radiation to identify malignant tumors, especially those not easily felt by hand.
A mammogram can also further investigate breast lumps that have already been identified, as well as other symptoms.
Mammography is not as effective in detecting breast cancer in younger, pre-menopausal women. Their breast tissue tends to be denser than that of post-menopausal women, and that makes their mammography results more difficult to read. Also, breast cancers appear white on a mammogram; young breast tissue is also white, but as the breast ages and turns to fat, it shows up dark on breast imaging, making the cancers easier to find.
As Dr. Susan Love has commented, “Looking for cancer on a young woman’s mammogram [is] like looking for a polar bear in the snow.”
Mammograms do not prevent breast cancer. They detect tumors, but they do not prevent you from getting tumors. Mammograms can miss more than 25 percent of all breast cancers, known as “false negatives.” Additionally, “false positive” results can occur — this is when a mammogram finds something in the breast that, on biopsy, proves not to be cancer. Research has shown that as many as 75 percent of all post-mammogram biopsy results turn out to be benign lesions.
Mammography screening initiated in the 1980s accounted for much of the increase in breast cancer diagnosis in the immediate years following. But what we now know is that early detection does not guarantee protection, and over- identifying problems that don’t need to be treated can lead to unnecessary biopsies and other invasive procedures. For more information, see Breast Cancer Screening Guidelines.
Digital images can be enlarged and the contrast adjusted, enabling radiologists to concentrate on suspicious areas. This improves their ability to detect tumors in dense breast tissue. Digital images can also be stored and transmitted electronically, making it easier to consult with experts at a distance.
For women under age 50, women who are premenopausal or perimenopausal, and women who have dense breasts, digital mammography may work better, but for most women over age 50, the use of digital mammography does not seem to catch cancers earlier or improve outcomes.
Ultrasound imaging, also called sonography, works by creating an image from reflected high-frequency sound waves emitted by a transducer, a microphone that helps magnify the sound. This technique excels in distinguishing solids from liquids, so it’s useful for differentiating solid tumors from fluid-filled cysts, which are benign.
Ultrasound may be used to evaluate abnormalities that appear on regular mammograms and can also be used to guide needle biopsies. Ultrasound is not useful as a screening tool by itself.
Automated whole-breast ultrasound devices have been shown in a large, well-designed study to significantly improve cancer detection in women with dense breasts, compared with mammography alone. This technique is generally not recommended for breast cancer screening in women of average risk, but may be used after masses are detected by palpation or mammography.
Magnetic Resonance Imaging (MRI)
Magnetic resonance imaging uses a powerful magnetic field and radio frequency pulses that are processed by a computer to create images of organs and tissues. It does not use ionizing radiation (X-rays) but does require an intravenous contrast injection.
MRI is quite effective in detecting invasive breast cancer, but it also can falsely identify benign lesions as malignant. It is not a substitute for regular mammography, nor is it for screening of the general population. It is sometimes recommended for screening women at very high risk for breast cancer.
Positron Emission Mammography (PEM)
Positron emission mammography uses gamma rays to detect “hot spots” of rapidly growing cells. A computer analyzes the image to determine the size, shape and location of the mass.
PEM is used in addition to mammography to identify small invasive cancers and ductal carcinoma in situ (DCIS), cancer that is confined to the milk ducts.
PEM is not yet widely available — its efficacy is still under study — and may not be covered by insurance. PEM may sometimes be used for preoperative assessment in breast cancer patients, but generally should not be used for screening or for following up on abnormal mammograms.
Breast-Specific Gamma Imaging (BSGI)
Breast-specific gamma imaging employs a radioactive tracer to identify cancer cells. Like PEM, it is used along with mammography and not instead of it.
BSGI is not widely available and needs more research to determine how well it works. It may not be covered by insurance.
In the future, as less invasive and more effective approaches are sought for early diagnosis and treatment of breast cancer, newer imaging technologies that look at breast cancer at the cellular level may become more widely used if there is clear evidence of their effectiveness as screening tools. Currently, BSGI and PEM involve fairly high doses of radiation and are therefore not appropriate for routine breast cancer screening. BGSI may sometimes be used for preoperative assessment in breast cancer patients.
Thermography records the temperature of different areas of the body by measuring infrared radiation. Malignant tissue generally has a higher temperature than normal tissue because of its richer blood supply and higher metabolic rate.
There is currently no evidence to support the use of thermography as a screening or diagnostic tool. In 2011, the FDA issued a safety alert stating that thermography should not be used as a stand-alone tool for breast cancer screening.
For years, experts advised women to perform monthly breast self-examinations (BSEs), believing that doing so would allow women to find potentially cancerous lumps and get diagnosed and treated for breast cancer more quickly. Unfortunately, scientific studies designed to measure the efficacy of BSEs have not found that women who perform BSEs are any less likely to die of breast cancer than women who don’t perform them.
For this reason, many medical guidelines and health organizations no longer recommend monthly BSEs. However, exploring your breasts is still a good way to get to know your body and become familiar with what is normal for you.
Breast Exam by a Health Care Provider
A clinical breast examination (CBE) is a physical examination of the breasts by a trained health care provider. Generally this happens during a routine annual check-up.
There is no evidence that CBE alone reduces breast cancer death rates, but this may be because there have been no trials that have looked at the use of only CBE, without mammography.
If you discover a lump in your breast, contact your health care provider. In addition to performing a clinical breast examination, she or he will refer you to further diagnostic testing. For more information, see What if I Have a Lump?