Most breast cancers are invasive. They do not stay inside the milk ducts or milk-producing glands but invade normal healthy tissue within and beyond the breast.
The number of women who die from breast cancer has been decreasing since 1989, due, in part, to early detection through screening and improved treatment.
What is a mammogram?
Breast screening technology has helped reduce the number of fatalities from breast cancer.
A mammogram is an X-ray image of the breast. Mammograms enable cancers to be screened when they are too small to be seen or felt and when there are no signs of symptoms of the disease. Mammograms do not prevent cancer but they make early detection possible.
Diagnostic mammograms can also check for breast cancer when there are signs and symptoms, such as a lump.
The American Cancer Society guidelines for the early detection of cancer recommend that women:
- Aged 40 to 44 years should be offered a yearly mammogram
- Aged 45 to 54 years should have an annual mammogram
- Aged 55 and older either continue yearly screening or have screening every 2 years
Women of all ages should be informed of the benefits, limitations, and potential harms of breast cancer screening.
Screening aims to detect:
- Calcium deposits in milk ducts and tissues
- Lumps or masses
- Asymmetric areas
- Dense areas in one breast or one area
- New dense areas that have appeared since a previous mammogram
Around 40 million mammograms are performed each year in the U.S.
What is tomosynthesis?
Tomosynthesis uses the same technology as regular mammograms, but while traditional mammograms are 2-D, tomosynthesis mammograms are 3-D.
Tomosynthesis differs from a regular mammogram just as a CT scan differs from an X-ray, or a ball differs from a circle. One is three-dimensional and the other is flat.
The U.S. Food and Drug Administration (FDA) have approved tomosynthesis for breast screening. However, as this is a new technology that is only available in limited hospitals, it is not yet considered the standard screening for breast cancer.
Similarities and differences between a mammogram and tomosynthesis
Standard 2-D mammography takes two X-rays of each breast. The X-rays are taken from two angles, from top to bottom and side-to-side. Tomosynthesis 3-D mammography takes multiple X-rays of each breast, and the X-rays are taken from many angles.
A mammogram takes two X-rays while tomosynthesis gathers data from various angles.
During both a standard 2-D and tomosynthesis 3-D mammography, a technologist will position the breast on the plate of the mammography machine. The top plate of the machine is lowered to compress the breast while a picture is taken.
Although the compression of the breast only lasts a few seconds, it can be painful or uncomfortable for some women.
During tomosynthesis, the X-ray tube moves in an arc around the breast. The machine takes around 11 images of thin slices of the breast from different angles in a 7-second examination. The information from the machine is then sent to a computer that assembles the cross-sectional data into 3-D images of the breast.
The X-rays from a 2-D mammography are only taken from two angles, which may create images with overlapping breast tissue. This overlapping breast tissue can be misinterpreted as a lump or mass.
3-D mammography creates images of the breast tissue in sections from multiple angles, which may make finding problematic breast abnormalities easier.
Tomosynthesis provides a clearer view and is more sensitive. In the U.S., tomosynthesis has reduced recall rates for further testing by 30 to 40 percent.
Researchers are currently unsure whether 3-D tomosynthesis mammograms are any better than 2-D mammograms, as there have been no quality studies that compare the accuracy of the two methods.
However, studies suggest that tomosynthesis might make cancer easier to see in dense breast tissue.
Benefits of tomosynthesis
Although further studies are needed, early evidence shows that compared to conventional mammography, tomosynthesis might provide:
- Earlier detection of breast cancers that are small or hidden
- Greater accuracy in locating abnormalities
- Less need for unnecessary biopsies and additional testing, resulting in 15 percent fewer false alarms
- More chance of finding multiple breast tumors
- Clearer images of dense breast tissue
- Reductions to the rate of false-positive readings
Disadvantages of tomosynthesis for breast screening
Possible problems with using tomosynthesis as a standard breast-screening tool include:
- Longer time to interpret images
- Over-diagnosis of conditions that would otherwise cause no harm
- Higher cost
- Double the radiation dose if combined with 2-D mammography
Although tomosynthesis may improve breast cancer screening, further studies are needed regarding the risks and benefits.
Risks of breast screening
The risks connected with mammograms and breast screening generally include:
- Exposure to low-dose radiation: However, the benefits of having mammograms regularly outweigh the risks.
- Inaccuracy: Depending on the technique used, the age of the person, and breast density, incorrect mammograms are possible.
- Difficulty interpreting: Younger women have more dense breast tissue compared with older women, so it is harder to see signs of cancer.
- Need for additional testing: Around 1 in 25 women will require further testing through ultrasound or biopsy.
- Not all cancers are detected: The cancer may be too small or in an area not visible on the mammogram. Around 1 in 5 cancers are missed by mammograms.
- Investigating harmless tumors: When cancers are found that would not have been life-threatening, unnecessary distress and treatment may result.
- Identifying incurable cancers: Aggressive tumors that can grow and spread rapidly to other body parts are difficult to treat.
Other breast cancer screening and testing
Other forms of breast screening and testing include:
- Clinical breast examination involves examination of the breasts by a doctor.
- Ultrasonography evaluates masses found in a mammogram.
- Magnetic resonance imaging (MRI) can be used for diagnostic evaluation, assessing masses after surgery or following radiation therapy. It can also be used for screening people who are at higher risk of breast cancer.
- Thermography shows skin temperature changes that could indicate a tumor.
- BRCA testing reveals whether a woman carries the BRCA1 or BRCA2 gene mutation that increases their risk of breast cancer. If a BRCA gene mutation is confirmed, more regular breast screening might be recommended.
Breast self-examination used to be recommended as part of the screening process, but it is no longer advised. Women are encouraged to be aware of the condition of their breasts and to report any unusual changes.
For now, 2-D mammography remains the gold standard for breast cancer screening and offers the best way to detect breast cancer early.