A mammogram is an X-ray of the breast used to diagnose changes in breast tissues and early signs of breast cancer. Mammograms can detect a lump or an abnormal growth in the breast that may indicate breast cancer. However, if breast tissue is dense, a small tumor may be missed.
According to the American Cancer Society (ACS), breast cancer has a 5-year survival rate of 99% when caught early. Regular mammograms can therefore help with early detection and decrease the risk of death.
The American College of Radiology (ACR) recommends annual screening mammograms for women over 40, regardless of symptoms or family history.
What are mammograms used for?
How is mammography done?
A mammogram is done by using an X-ray machine that uses low-dose radiation. The machine has two plates that flatten the breast to spread the tissues apart so that the X-rays can pass through them easily.
The technician will place the breast on a plastic plate, another plate will press the breast firmly from above (flattens the breast) and an X-ray is taken. The same steps are repeated to take an X-ray from a side view and for another breast. The technician will check all four X-rays to make sure they are clear and readable.
A radiologist will read the mammogram and look for early signs of breast cancer or other problems.
For many women, a mammogram can be uncomfortable because the X-ray plates tightly squeeze the breast tissue. Discomfort typically lasts for just a few minutes, although this depends on factors such as breast size and the experience of the technician.
What are the potential drawbacks of a mammogram?
Mammograms are generally safe because they expose the breast tissue to a very low dose of radiation. The total dose for a mammogram with two views of each breast is about 0.4 mSv.
However, there are potential drawbacks to screening mammography:
- False-positive result: False-positive results occur when abnormally dense but normal tissue is misdiagnosed as cancer. False-positive results may occur in younger women with dense breasts, previous breast biopsies and a family history of breast cancer, and who are on estrogen (menopausal hormone therapy). This could lead to an unnecessary biopsy.
- False-negative result: False-negative results occur when the mammogram appears normal even though cancer is present. Fibroglandular tissue and tumors have a similar density (both appear as white areas); tumors are harder to detect in women with dense breasts. False-negative results can delay treatment.
- Overdiagnosis: Sometimes, small cancers that are not life-threatening may be diagnosed, resulting in overtreatment or unneeded treatment.
- Radiation exposure: Though mammograms use only small doses of radiation, repeated X-rays are potentially harmful.
What does a mammogram result show?
The American College of Radiology (ACR) has established a uniform way for radiologists to evaluate mammogram findings through a system called breast imaging reporting and database system (BI-RADS), which includes 7 categories.
|0||Additional imaging required||To assign a category, additional imaging is needed|
|I||Negative||Continue regular screening mammograms|
|II||Benign findings (noncancerous)||Continue regular screening mammograms|
|III||Probably benign (not sure)||6-month follow-up mammogram|
|IV||Suspicious abnormality||Biopsy may be required|
|V||Highly suggestive of cancer (malignancy)||Biopsy required|
|VI||Known biopsy-proven cancer||Biopsy to confirm cancer before treatment initiation|
Breasts are made up of both glandular and connective tissues, together called fibroglandular and fatty tissues. Breast density reflects the amount of fibrous and glandular tissue compared to the amount of fatty tissue in the breasts. BI-RADS also includes four categories of breast density:
- Almost entirely fatty
- Scattered areas of fibroglandular density
- Even density throughout, excess areas of fibroglandular density
- Extremely dense, making it difficult to visualize tumors
The first two categories are considered low-density breasts, whereas the last two categories are considered high-density breasts.
Women with dense breasts have a higher risk of getting breast cancer.
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Where does breast cancer start?
Breasts are made up of three parts.
- Lobules: Milk-producing glands
- Ducts: Tubes that carry milk to the nipple
- Connective tissue (fibrous and fatty tissues): Surrounds other structures
Most often, breast cancer begins in the lobules or ducts and may metastasize (spreads to other organs) through blood and lymph vessels.
What are different types of breast cancer?
- Invasive ductal carcinoma: Cancer begins in the ducts and spreads to other breast tissues and parts of the body.
- Invasive lobular carcinoma: Cancer cells begin in the lobules and spread to other breast tissues and parts of the body.
Ductal carcinoma in situ is a condition preceding breast cancer, wherein the cancer cells are present only in the duct lining and have not spread to the other tissues.
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Centers for Disease Control and Prevention. What is a Mammogram? https://www.cdc.gov/cancer/breast/basic_info/mammograms.htm
National Cancer Institute. Mammograms. https://www.cancer.gov/types/breast/mammograms-fact-sheet
Nazario B. Breast Cancer Screening and Diagnosis. WebMD. https://www.webmd.com/breast-cancer/breast-cancer-detection
Pichardo G. Breast Cancer and Mammograms. WebMD. https://www.webmd.com/breast-cancer/mammograms
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