No, the Radiologist Does Not Think This Is a Tumor
The BI-RADS 0 classification explicitly indicates the radiologist cannot yet determine whether this asymmetry represents a tumor—it requires additional imaging evaluation before any diagnostic conclusion can be made. 1
Understanding BI-RADS Category 0
A BI-RADS 0 designation means "incomplete assessment" and is specifically used when a finding requires additional evaluation before the radiologist can make any determination about its nature. 1 This category is almost always assigned in screening situations and indicates that the current images are insufficient to characterize the finding. 1
The radiologist is not stating or implying this is a tumor—they are stating they need more information to make that determination.
What the Asymmetry Could Represent
The differential diagnosis for a mammographic asymmetry is broad:
Most Likely Benign Causes (>75% of cases):
- Summation artifact from overlapping normal breast tissue (the most common cause, accounting for the majority of asymmetries) 2, 3
- Fibrocystic changes 4
- Stromal fibrosis 4
- Fat necrosis 4
- Intramammary lymph nodes 3
Malignant Possibilities:
- Invasive breast cancer can present as an asymmetry, though this is less common than the classic spiculated mass appearance 5, 6
- Low or intermediate-grade DCIS can present as asymmetry without calcifications 7
- The malignancy rate for developing asymmetries ranges from 12.8% at screening to 20-42.9% when biopsy is ultimately recommended 7, 4
Required Next Steps Per Guidelines
The National Comprehensive Cancer Network and American College of Radiology recommend the following algorithmic approach: 7
Step 1: Diagnostic Mammography with Additional Views
- Spot compression views to determine if the asymmetry persists or disappears (summation artifact) 7, 6
- Magnification views if any associated microcalcifications are present 7
- Rolled views (medially/laterally in CC projection) can effectively differentiate summation artifacts from real lesions in 74.6% of cases 3
Step 2: Targeted Ultrasound
- Should be performed concurrently with diagnostic mammography 7
- Identifies potentially benign causes (cysts, lymph nodes) or provides a target for biopsy 7, 6
- Critical caveat: 23.8% of cancers presenting as developing asymmetry have no sonographic correlate, so negative ultrasound does not exclude malignancy 7
Step 3: Determine Final BI-RADS Category After Complete Workup
- BI-RADS 1-3: Clinical re-examination in 3-6 months, follow-up imaging every 6-12 months for 1-2 years to assess stability 7
- BI-RADS 4-5: Tissue biopsy required (core needle biopsy preferred) 7
Critical Clinical Pitfalls
- Never assume an asymmetry is benign without complete diagnostic workup, as malignancy rates can reach 20-43% when biopsy is ultimately recommended 7, 4
- Absence of ultrasound findings should not preclude biopsy if mammographic features remain suspicious after additional views 7, 6
- If the asymmetry is associated with suspicious microcalcifications, architectural distortion, palpable abnormality, or is new/increasing compared to prior studies, biopsy is indicated regardless of ultrasound findings 7
- Digital breast tomosynthesis has shown that developing asymmetries without sonographic correlate have a 20% malignancy rate, higher than traditional digital mammography 4