A mammogram is a safe, low-dose x-ray of the breast that can pick up very small breast cancers, well before a lump can be felt.
Women have a 95% chance of surviving breast cancer five years or longer if the cancer is detected by a mammogram. Because the risk of breast cancer increases as you get older, BCFNZ recommends women consider having regular screening mammograms from the age of 40.
What is a screening mammogram?
A screening mammogram is an x-ray of the breasts to detect breast cancer before it shows any signs or symptoms. Early detection can reduce the chance of dying from breast cancer by approximately one third, as small, early cancers are easier to treat. Screen-detected cancers are also more likely to be treated without having to completely remove the breast.
Having regular screening mammograms can’t prevent breast cancer but can detect it early and reduce (but not completely eliminate) the risk of dying from the disease.
A mammogram is currently the most accurate method of breast screening but can’t give an absolute guarantee that cancer is not present, because some cancers are harder to see on mammography and dense breast tissue can make mammograms harder to “read”.
Previously, mammogram pictures were stored on film but digital mammography is now used and images are stored and viewed on a computer, allowing radiologists to enlarge certain areas to examine them more closely. This improved technology has increased breast cancer detection rates.
Breast tomosynthesis or 3D mammography is a newer technology which takes multiple low dose X-rays of the breast then creates a 3 dimensional picture on a computer. This uses more radiation than standard 2D mammography but may give a clearer picture, detect more cancers and reduce recalls for further testing.
What happens during a mammogram?
An MRT (medical radiation technologist) or radiographer will place your breast between two plates on the mammogram machine. The breast is then compressed to spread the tissue apart. This gives a clearer view, and adequate compression lessens the amount of radiation that needs to be used. Some people find this a bit uncomfortable, but it doesn’t last long. It is best to go for a mammogram after your menstrual period has finished and any breast tenderness has subsided.
Normally two views are taken on a screening mammogram, one from the side and one from above. The images are reviewed by two radiologists (specialist doctors who use medical imaging to diagnose disease) who issue a report describing the findings. If anything abnormal is found you will be recalled for further investigation.
Where do I have my mammogram?
BreastScreen Aotearoa (BSA) is New Zealand’s free National Breast Screening Programme. They provide free mammograms every two years for women with no symptoms aged between 45 and 69 (and have recently announced they'll be progressively increasing this upper limit, from 69 to 74).These are provided at BSA's contracted fixed sites and also at mobile screening units.
To find out where to have a Breastscreen Aotearoa mammogram visit their website:
Screening mammograms can also be done at:
- Private x-ray clinics
- Private breast clinics
Public hospitals (only for women who are at high risk. Surveillance screening is done for women who have previously had breast cancer.)
You may wish to have a support person or whanau member go with you.
How much does a mammogram cost?
- Breastscreen Aotearoa provides free mammograms for women with no symptoms of breast cancer, between the ages of 45-69 (with the upper limit to be "progressively increased" to 74 years of age).
Will I get a reminder about my next mammogram?
Once you have registered with BreastScreen Aotearoa they will contact you before your next mammogram is due. Most private breast clinics and family doctors also have a recall system, but it probably pays to ask for one at reception to ensure you get a reminder each year.
What is a diagnostic mammogram?
Mammography is also used as a diagnostic tool if an abnormality has been found on a clinical breast examination or on a screening mammogram. Diagnostic mammograms take extra views and use magnification to get a closer look at the abnormality.
How does breast density affect mammography?
Young women have a higher proportion of glandular and fibrous tissue compared to fatty tissue. These tissues appear “dense” and have a light grey or white appearance on a mammogram, while fatty tissue appears darker. Cancers also appear light grey or white so this can make them more difficult to detect amongst the background tissue. This is why mammography is not routinely used for breast screening in young women under the age of 40 (except for those at very high risk due to family history or confirmed genetic mutation).
The proportion of dense glandular tissue naturally declines after menopause making mammograms easier to read. However, women taking Hormone Replacement Therapy (HRT) have higher breast density ,making mammography results less accurate.. Annual screening is recommended in this group.
Women with high breast density may also be recommended to have annual rather than two-yearly screening.
What are interval cancers?
Breast cancers which are diagnosed between breast screening tests are called interval cancers. In some cases they may have grown very quickly, or they may have been present but not detected on the last screening.
What are false negatives and false positives?
Unfortunately, there is no foolproof breast screening method. Normal breast tissue can sometimes mask a breast cancer so it can’t be seen on a mammogram, and occasionally a detectable cancer will be missed. This is known as a false negative result.
Mammograms can also identify an area that looks like cancer, but further testing proves it to be benign. This is a false positive result.
What are the risks of radiation exposure from a mammogram?
The dose of radiation used in a two view mammogram is thought to be equivalent to the amount of radiation absorbed from natural surroundings (background radiation) over a period of about seven weeks. The dose is lower than that of a standard chest X-ray.
The benefit of early detection of a breast cancer is believed to outweigh the risk of this small exposure to radiation.
Can I screen with ultrasound instead?
Ultrasound uses sound waves to create an image and does not involve radiation. It is very useful for adding extra information about a targeted area of abnormality found on mammogram or clinical examination, but is not recommended as a primary breast screening scan. While it is very sensitive, it is less specific than mammography and leads to a higher proportion of false positive results. Calcifications, which can represent ductal carcinoma in situ are usually not detected by ultrasound.
What about MRI?
MRI (magnetic resonance imaging) of the breast uses a powerful magnet, radio waves and a computer to produce detailed images of the breast. An injection of a contrast medium (Gadolinium) is often used to assist detection. MRI is mostly used as a supplementary tool in breast cancer detection, after mammography and ultrasound. It is often used to evaluate the extent of disease and is the best method of determining whether silicone implants have ruptured.
It may be recommended in addition to mammography for screening women who are at high risk of breast cancer due to family history or known gene mutation, but is not generally used in regular breast screening. MRI is a costly procedure which takes more time to perform than other imaging methods and requires specially trained radiologists to review the images.
What are the harms and benefits of breast screening?
Breast screening might diagnose some slow growing cancers which may never have caused any harm over a person’s lifetime. This is known as overdiagnosis. Unfortunately there is currently no way for doctors to know which cancers fall in to this category.
- Exposure to small amounts of radiation (see above).
- Anxiety caused to women who are recalled for further testing but are found not to have cancer.
Despite these potential harms, large scale studies have shown that on a population level, the benefits of breast screening outweigh the harms. Mammograms are still the best way of detecting breast cancer early, before it shows any symptoms and while it is more easily treated. Breast screening can save lives and save breasts.
How does the free screening process work?
To find out what to expect, see the National Screening Unit's interactive guide: