Are asymmetric breasts a sign of cancer?

Annual or biennial mammograms are essential to a woman’s breast health because they detect early signs of cancer or abnormalities. A common abnormality seen on mammogram results is breast asymmetry.

Breast asymmetry is usually no cause for concern. However, if there’s a large variation in asymmetry or if your breast density suddenly changes, this could be an indication of cancer.

Breast asymmetry occurs when one breast has a different size, volume, position, or form from the other.

Breast asymmetry is very common and affects more than half of all women. There are a number of reasons why a woman’s breasts can change in size or volume, including trauma, puberty, and hormonal changes.

Your breast tissue can change when you’re ovulating, and can often feel more full and sensitive. It’s common for the breasts to look bigger because they actually grow from water retention and blood flow. However, during your menstrual cycle, they’ll return to normal size.

Another cause for asymmetrical breasts is a condition called juvenile hypertrophy of the breast. Though rare, this can cause one breast to grow significantly larger than the other. It can be corrected with surgery, but it may lead to a number of psychological issues and insecurities.

It’s common for two breasts to be different sizes, but they’re usually similar in density and structure. Doctors use mammograms, a type of breast exam, to evaluate the internal structure of the breast.

If your mammogram shows you have asymmetrically dense breasts, the difference in density could be classified into one of four categories if a mass is found:

  1. Asymmetry. Your breasts are only evaluated using one projection. These images aren’t reliable because they are one-dimensional. Overlapping dense structures in the breast could be difficult to see. If your doctor finds a lesion or abnormality, they’ll call for another three-dimensional imaging test.
  2. Global asymmetry. This finding shows there’s more volume or density in one breast than the other. Global asymmetry findings are normally the result of hormonal changes and normal variation. If a mass is found, your doctor will request additional imaging.
  3. Focal asymmetry. These images show a density on two mammographic views, but your doctor can’t fully tell if it’s a true mass. They’ll request further imaging and evaluation to rule out cancerous or abnormal masses.
  4. Developing asymmetry. This asymmetry type indicates a significant change between past and current exams. The density may be new, or could have increased. These findings are enough to raise suspicion of potentially malignant cells.

If your mammogram indicates asymmetry, your doctor will need additional images to determine if the change in shape or density is normal.

The first step is to compare past mammogram images for changes in shape or density. If you’ve never had asymmetric breasts or if your asymmetry has increased over time, your doctor will request extra tests.

Breast ultrasound

Your doctor may request a breast ultrasound. This method helps to diagnose abnormal findings from obscure mammogram images. A breast ultrasound uses sound waves that produce pictures of your breasts’ internal structure.

The breast ultrasound images can help determine if the mass is benign, a fluid-filled cyst, or if it’s potentially a cancerous tumor. In some cases, a mass can be both solid and fluid-filled.

Breast MRI

Magnetic resonance imaging (MRI) of the breast is a test used to help detect breast cancer or other abnormalities. While in some cases this test is used after a biopsy has confirmed cancer, breast MRIs can be used alongside mammograms to screen for breast cancer.

This is specifically helpful for women with a high risk of breast cancer from family history or heredity.


If your imaging test results come back abnormal, or if your doctor suspects the abnormality is cancerous, the next step is to have a biopsy. During this procedure, a portion of your affected breast tissue is removed for further testing and to check for cancer.

If the biopsy comes back negative, doctors recommend regular breast exams to monitor any change. If the biopsy comes back positive, your doctor will talk with you about treatment options.

Breast asymmetry is a common characteristic for women, and is often no cause for concern. However, if the size of your breasts change or the density variation becomes larger over time, these changes could indicate something is wrong.

Research is still being conducted on the relationship between asymmetric breasts and cancer risk. Some studies have shown women with breast cancer had a greater breast asymmetry, combined with other risk factors such as heredity and age, than women who were healthy. Further research is still needed.

If you have a predisposition to cancer from family history or if you notice irregular changes in your breasts, you should discuss your concerns and options with your doctor.