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Women's Health

Screening for cancer: Mammography

Mammography is the most common method for detecting abnormalities in the breast. This screening technique is an x-ray that uses very low levels of radiation. It can find 85%–90% of breast cancers. Mammography makes it possible to see tiny cancers that may measure as little as half a centi­meter (about one-fifth of an inch). Generally, a lump can't be felt until it's at least twice that size. The abnormalities that show up on a mammogram may be benign or malignant.

Research shows that annual screening mammography performed on large populations of women who otherwise have no breast complaints may save lives in women ages 50 and older and suggests that it possibly reduces mortality in women ages 40–49. The American Cancer Society and other medical groups recommend that women have an annual mammogram starting at age 40. Women who are at high risk for breast cancer because of a family history or other factors may begin screening at an earlier age. (A family history of breast cancer may raise the possibility of performing genetic testing.) The downside of mammography is that it has increased the number of surgical biopsies in women who do not have breast cancer, and may increase a patient's anxiety level. As with any surgical procedure, complications may occur following a biopsy.

Figure 3: What the radiologist sees

The radiologist evaluating your mammogram may need to distinguish between a benign (noncancerous) mass and a suspicious mass. A benign mass (A) may appear as a low-density (translucent) area with clear borders. A suspicious mass (B) is more likely to be denser (more opaque) and to have irregular borders that radiate outward in a star-like pattern. The radiologist will also look for the small white dots known as calcifications. Tiny calcifications that appear in gravel-like clusters in one part of the breast (C) are considered suspicious while larger calcifications scattered individually throughout the breast are more likely to be benign. The finding of microcalcifications may indicate the presence of ductal carcinoma in situ.

The mammography procedure. To obtain a clear picture of the breast tissue, a technician will ask you to stand with your breast on a platform and will pull the breast away from your body so the image can show as much breast tissue as possible.

The machine will compress your breast briefly between two plastic plates while it takes the x-ray picture. As soon as the x-ray is made, the plates automatically release. Horizontal and vertical views are made of each breast. Some women find the compression painful; most find it merely uncomfortable. Fortunately, the compression lasts only seconds.

If certain areas of the breast don't show up clearly on the mammograms after the initial reading by the radiologist (a doctor who specializes in interpreting these types of images), the technician may need to take additional views. This happens in 5%–10% of screening mammograms. Afterward, you will either be asked to wait until the radiologist has read each film, or you will receive the results in the mail a few days later.

If the results indicate a concern, the center will contact you by phone rather than mailing the results. It is important that you contact the radiologist or physician who ordered the mammogram if you have not been contacted about your results within a week. Although uncommon, letters in the mail may be lost or some other error may occur in getting results to you.

On a mammogram, the structures inside your breast appear in shades ranging from white to black. The white areas are mainly milk ducts. The hazy gray and black areas are fat tissue. Abnormalities appear as white spots of two types: densities or calcifications.

Densities. These abnormalities appear as light spots on the mammogram. If a density appears on a mammogram, the radiologist will examine it with two or more different mammographic views. A density may or may not indicate cancer. A density with a starburst shape (arms radiating outward from the center) is called "spiculated" and often indicates cancer. Noncancerous densities usually appear as a spot with a smooth outline and no arms radiating outward. If a density appears on a mammogram, the next step is usually a breast ultrasound.

Calcifications. These abnormalities appear as tiny, sand-grain-sized bright white dots. Most calcifications are benign. Benign calcifications are usually scattered randomly through both breasts, almost like a snowstorm. Or, benign calcifications may be clustered in a small space and are usually similar in size and may be coarse in appearance. If the calcifications appear to be benign, you and your doctors can monitor any further changes with yearly mammograms. Calcifications that appear as tiny dots of different sizes and shapes (pleomorphic) in a line (linearly arranged) are likely inside a duct and generally indicate cancer. More than 70% of suspicious mammographic findings that are biopsied turn out to be benign.

BI-RADS assessment categories

  • Category 0: Needs additional imaging

  • Category 1: Negative

  • Category 2: Benign finding

  • Category 3: Probably benign finding — shorter mammogram schedule (usually six months)

  • Category 4: Suspicious abnormality; biopsy should be considered

  • Category 5: Highly suggestive of malignancy; biopsy warranted

Assessing the mammogram. Radiologists use standard terminology for classifying the findings of a mammogram. The radiologist will use numbered categories to refer to the shape and margins of a mass, the appearance and distribution of calcifications, and the radiologist's level of suspicion that the abnormality represents a breast cancer. Such a classification system provides a common language for communication between radiologists, clinicians, and the women having the mammograms, regardless of where the procedure has been done. The categories were developed by the Breast Imaging Reporting and Data System. It is very likely that the letter you receive from either the radiologist or your physician who ordered the mammogram will include the BI-RADS scoring system in their report to you.

Date Last Reviewed: 4/12/2007
Date Last Modified: 4/23/2007
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