What Exactly Is Asymmetry?
Breast asymmetry on a mammogram does not mean your breasts look different in the mirror - nearly all women have some difference in breast size. On a mammogram, "asymmetry" is a specific radiology term referring to a region of increased fibroglandular density visible on one side that doesn't have a corresponding area on the other side. It is not a three-dimensional mass.
The most common cause is summation artifact - natural superimposition of normal breast tissue layers that temporarily looks like more tissue is present when viewed from one angle. Additional views usually make it disappear.
Why This Can Feel Confusing
- Asymmetry is a common finding and is often due to normal differences in breast tissue, but it can sometimes require additional evaluation.
- Determining whether it is significant depends on comparison with prior imaging and subtle changes that may not be obvious without context.
I review your imaging report and explain what these findings mean in clear, simple terms — so you understand what's important and what happens next.
Upload My ReportIs This Cancer?
Most asymmetries are not cancer and are often due to normal differences in breast tissue.
In some cases, an asymmetry can be the only sign of a type of breast cancer called invasive lobular carcinoma (ILC), which tends to grow in a more subtle, diffuse pattern rather than forming a distinct lump.
Because of this, a new or developing asymmetry is usually evaluated more closely with additional imaging to better understand what it represents.
Common Next Steps
Should I Be Concerned?
- Most asymmetries are benign (non-cancerous) and simply reflect normal variation in breast tissue.
- A closer look may be needed if the asymmetry is new, changing, or does not resolve with additional imaging.
- In most cases, this involves extra imaging to better understand the finding. A biopsy is only recommended if the finding remains unclear or concerning after imaging.
Related Topics
Does your report mention asymmetry? Identifying which type is described - and what BI-RADS category was assigned - tells you exactly what to expect. A board-certified radiologist with subspecialty breast imaging experience can walk you through it step by step.
Get My Report Explained