A mammogram report indicating “focal asymmetry” is an area in one breast that appears denser or different from the area in the other breast. While common and often not indicative of cancer, it signals that further investigation is necessary.
What Is Focal Asymmetry?
Focal asymmetry describes a localized area in one breast that shows increased tissue density compared to the opposite breast. Unlike a defined mass, it lacks the distinct borders or three-dimensional shape typically associated with a lump. It must be visible on at least two different mammogram views (angles) to be classified as focal asymmetry.
This appearance often results from normal overlapping breast tissue, known as a summation artifact, where healthy breast structures create perceived density. Focal asymmetry is a frequent finding, appearing in about 21% of all mammograms. It warrants additional imaging to determine its cause, rather than being a diagnosis in itself.
What It Might Indicate
Focal asymmetry can represent a range of conditions, most of which are benign. It often reflects normal variations in breast tissue composition, where one area contains more glandular or fibrous tissue. Hormonal fluctuations can influence breast tissue density. Benign changes like cysts, which are fluid-filled sacs, or fibrocystic changes, characterized by lumpy or rope-like breast tissue, manifest as focal asymmetry. Prior breast surgeries or injuries can result in scar tissue that appears as an area of increased density.
While most cases are benign, a smaller percentage of focal asymmetries are associated with conditions needing attention. These might include benign but significant findings such as radial scars, which can sometimes mimic cancer, or papillomas, which are small, non-cancerous growths in the milk ducts. Less commonly, focal asymmetry can be an early indicator of breast cancer, including invasive ductal carcinoma or invasive lobular carcinoma. When a focal asymmetry is new or appears to have grown compared to previous mammograms, it is termed a “developing asymmetry” and carries a slightly higher potential for malignancy.
Next Steps for Diagnosis
When a focal asymmetry is identified on a screening mammogram, additional imaging tests are typically recommended. The first step often involves specialized mammographic views, known as spot compression mammography. This technique applies localized compression to spread out overlapping breast tissue and better visualize the finding.
Following spot compression, an ultrasound of the breast is commonly performed. Ultrasound uses sound waves to create images of the breast tissue, helping determine if the asymmetry is a solid mass, a fluid-filled cyst, or dense normal tissue. If findings remain unclear after mammography and ultrasound, or if other concerning factors exist, a breast Magnetic Resonance Imaging (MRI) might be considered. These tests help characterize the asymmetry and guide decisions about a biopsy.
Understanding Your Results and Next Steps
After undergoing additional diagnostic imaging, the results determine the next course of action. In many cases, the focal asymmetry is found to be benign. If confirmed as benign, routine follow-up mammograms are typically recommended.
If the asymmetry remains suspicious after additional imaging, or if certain characteristics are identified, a biopsy may be recommended. A biopsy involves removing a small tissue sample from the area of concern for microscopic examination by a pathologist. The biopsy results provide a definitive diagnosis—benign, high-risk, or malignant—guiding any necessary monitoring or treatment.