is asymmetry on mammogram common?

A radiologist will examine a mammogram to look at the difference in position, volume and form of the breasts. In most cases, the breasts are generally symmetric in their density and architecture, but sometimes a report may reveal asymmetric density, which is common and usually noncancerous.

The criteria for an asymmetry include that it is seen only on one projection, the borders are not convex, or the center is not denser than the periphery (e.g. it is interspersed with fat).

Under the BI-RADS lexicon 5, there are four types of asymmetries:

The most common cause for an asymmetry on screening mammography is superimposition of normal breast tissue (summation artifact) 6. Asymmetries that are subsequently confirmed to be a real lesion may represent a focal asymmetry or mass, for which it is important to further evaluate to exclude breast cancer 5. Developing asymmetries are sufficiently suspicious to justify recall and biopsy, with 15% representing malignancy 7.

Global asymmetry is most commonly a normal variant and is discussed separately.

The BI-RADS lexicon defines four types of asymmetries 5:

An asymmetry or focal asymmetry that is unchanged over at least 2 years does not deserve attention. Otherwise, findings of an asymmetry, focal asymmetry, or developing asymmetry found on screening merit recall for further evaluation.

Upon recall from screening mammography, repeating the original view(s) with the finding is often helpful and additional views should be considered:

In the diagnostic setting, localized findings can be further evaluated by ultrasound.

Asymmetries that turn out to be summation artifact are benign (BI-RADS 2). The BI-RADS Atlas offers guidance regarding the other categories of asymmetries 5:

A solitary focal asymmetry (without architectural distortion, calcifications, or underlying mass identified on diagnostic mammography and ultrasound) is assessed as BI-RADS 3 (likely benign).

A developing asymmetry, unless shown to be characteristically benign such as a cyst on ultrasound, is assessed BI-RADS 4 (suspicious). An exception would be if there is a clear benign explanation, such as recent surgery, trauma, or infection at that site.

Global asymmetry, in the absence of palpable correlate, is assessed BI-RADS 2 (benign).

Asymmetries may represent any of a long list of pathologies:

However, a significant variation or sudden change in aspects, such as density, could indicate a problem. Discuss the results with your healthcare provider.

Learn more about breast asymmetry, its causes, how it relates to cancer, testing, and more.

Asymmetry results on a mammogram indicate that the image shows something different on one breast than the other or to other parts of that same breast.

Types of breast asymmetry seen on a mammogram include:

Focal asymmetry: A difference in the breast seen on two or more mammogram images.

Developing asymmetry: Focal asymmetry that appears to grow or change compared to previous tests.

Global asymmetry: More breast tissue in one breast or one area of a breast.

When breast asymmetry is detected, additional testing may be recommended. However, this does not mean that breast asymmetry is cancerous.

Benign causes of breast asymmetry on mammogram include the following:

It is unclear how breast asymmetry impacts cancer risk, and it may depend on the cause of breast asymmetry. For example, fibrocystic changes do not increase cancer risk, nor does pseudoangiomatous stromal hyperplasia.

Stromal fibrosis can increase the risk of breast cancer and may be associated with inaccurate biopsies. This can happen when non-cancerous stromal fibrosis is located next to cancerous cells; a biopsy sample containing the non-cancerous stromal fibrosis is taken without catching any cancerous cells.

While breast asymmetry is not usually indicative of cancer, medical professionals may recommend testing to be sure.

When breast asymmetry is found on a mammogram, additional screening tests are usually recommended to rule out breast cancer. Further testing should not be a major reason for concern; many people with breasts who have a screening mammogram are asked to undergo additional testing, and less than 10% of them receive a breast cancer diagnosis. The type of further testing depends on what is found on the screening mammogram.

A diagnostic mammogram is similar to a screening mammogram but with additional images of the asymmetric area. 3D tomosynthesis, which uses X-ray technology like a mammogram, can take images from more angles, providing a more accurate result. Sometimes a combination of additional tests is recommended.

Breast asymmetry is usually entirely normal and does not indicate an increased risk for cancer. However, it is important to see your healthcare provider for an evaluation and follow through with any recommended testing.

If the initial mammogram result of breast asymmetry does lead to a breast cancer diagnosis, it is a treatable condition with high survival rates.

Breast asymmetry means that breasts are of different sizes or shapes. When found on a mammogram, breast asymmetry means that there is a difference in one area of one breast in comparison to the rest of the breast, such as an area of breast tissue that is denser. While this can be a sign of cancer, it is normal to have some breast asymmetry; it is usually not cancer.

Even so, additional testing, such as a diagnostic mammogram or 3D tomosynthesis, may be recommended to ensure breast cancer is not overlooked.