What Does Asymmetry on a Mammogram Report Mean?

Breast asymmetry on a mammogram report means that part of the breast looks different from other parts of the same breast or the other breast. This is often due to benign (not harmful) changes.

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.

A healthcare provider is discussing an asymmetry mammogram with a person.
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Asymmetry on Mammogram Results

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.

Causes of Breast Asymmetry

Benign causes of breast asymmetry on mammogram include the following:

  • Fibrocystic changes: Cysts filled with fluid and scar tissue in the area of the cysts
  • Dense stromal fibrosis: The connective tissue in that area of the breast is denser than it is in other areas
  • Pseudoangiomatous stromal hyperplasia: A lump of non-cancerous cells that grows in the breast

Breast Asymmetry Causes

  • Growths, such as fibroids or cysts
  • Dense breast tissue
  • Lumps or masses

Is Asymmetry a Sign of Cancer?

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.

Additional Screening Tests

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.

Types of Additional Screening for Breast Asymmetry

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.

A Word From Verywell

Breast asymmetry is entirely normal and not cancerous most of the time. If you or someone you know suspects or has been told they have breast asymmetry, help is available. Reach out to a healthcare provider, such as a gynecologist, oncologist, or primary healthcare provider. If breast asymmetry does lead to a breast cancer diagnosis, know that it is a treatable condition with high survival rates.

Frequently Asked Questions

  • Does asymmetry on a mammogram mean cancer?

    No, breast asymmetry on a mammogram does not mean cancer. However, while it is usually completely normal and harmless, it can occasionally lead to a breast cancer diagnosis, so it is essential to follow through with any recommended additional testing.

  • How common is asymmetry of the breasts?

    No two breasts are the same, and most women have breasts that are different in size by 15% to 20% or more. Yet, over 10% of mammogram results come with recommendations for additional testing, and less than 10% of those who get further testing end up with a breast cancer diagnosis.

  • Does asymmetry of the breast go away on its own?

    Depending on the cause of breast asymmetry, it can go away on its own. For example, breasts can grow unevenly during puberty and then become more symmetrical by the end of puberty. Sometimes they remain asymmetrical and never lead to any issues.

11 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
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  2. American Cancer Society. What does the doctor look for on a mammogram?

  3. American Academy of Family Physicians. Is asymmetric breast tissue a sign of malignancy?

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  6. Malik N, Lad S, Seely JM, Schweitzer ME. Underestimation of malignancy in biopsy-proven cases of stromal fibrosisBJR. 2014;87(1039):20140182. doi:10.1259/bjr.20140182

  7. American Cancer Society. Getting called back after a mammogram.

  8. Mokhtar O, Abd elsalam S, Gamal G, et al. 3d digital breast tomosynthesis versus us in evaluating breast asymmetriesEgyptian Journal of Radiology and Nuclear Medicine. 2020;51(1):110. doi:10.1186/s43055-020-00196-0

  9. University of Utah Health. My breasts are different sizes - am I normal?

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By Ashley Olivine, Ph.D., MPH
Dr. Ashley Olivine is a health psychologist and public health professional with over a decade of experience serving clients in the clinical setting and private practice. She has also researched a wide variety psychology and public health topics such as the management of health risk factors, chronic illness, maternal and child wellbeing, and child development.