What are the signs of breast cancer on a mammogram?

Mammographic Signs of Breast Cancer

The most highly suggestive mammographic signs of breast cancer are spiculated masses and pleomorphic microcalcifications, which carry a ≥95% probability of malignancy. 1

Primary Malignant Features

Masses

• Spiculated masses are the classic mammographic appearance of invasive breast cancer, presenting as irregular densities with radiating lines extending from the margins 1, 2
• Irregular masses with indistinct or microlobulated margins should raise suspicion for malignancy 2
• Masses associated with architectural distortion, particularly when combined with calcifications, warrant immediate biopsy 1, 3

Calcifications

• Pleomorphic (varying size and shape) microcalcifications are highly suspicious for malignancy, particularly when clustered or grouped 1, 4
• Fine linear or fine-linear branching calcifications are characteristic of high-grade ductal carcinoma in situ (DCIS) with necrosis 2
• Calcifications are the most common finding in DCIS, present in approximately 80-90% of cases 1, 2
• The distribution pattern matters: irregular or triangular clusters suggest segmental or ductal distribution, which is more concerning for malignancy 1

Architectural Distortion

• Focal distortion of normal breast architecture without a visible mass can indicate malignancy 1
• This finding may represent invasive carcinoma with fibrosis or even DCIS with associated sclerosis 3
• Architectural distortion is a subtle but important sign that requires additional evaluation 5

Secondary Suspicious Features

Asymmetries

• Focal asymmetry (density present in one breast but not the corresponding area of the other) requires further evaluation 1, 6
• Developing density (new or enlarging asymmetry on serial mammograms) is particularly concerning 5
• Most asymmetries are benign summation artifacts, but persistent asymmetry after additional views warrants diagnostic workup 6

Soft Tissue Changes

• Skin thickening, particularly when diffuse and associated with trabecular distortion, can indicate inflammatory breast cancer 1
• A single dilated duct may be an early subtle sign of malignancy 5

BI-RADS Classification Framework

The American College of Radiology BI-RADS system provides standardized risk stratification: 1

• BI-RADS 5 (Highly Suggestive of Malignancy): ≥95% probability of cancer; includes spiculated masses and malignant-appearing pleomorphic calcifications 1
• BI-RADS 4 (Suspicious): Wide range of malignancy probability, greater than 2% but less than 95%; biopsy should be considered 1
• BI-RADS 3 (Probably Benign): <2% risk of malignancy; includes noncalcified circumscribed masses, focal asymmetries, and clusters of round calcifications 1

Critical Clinical Pitfalls

• Never allow negative imaging to override a clinically suspicious palpable mass—any highly suspicious finding on physical examination requires biopsy regardless of imaging results 2
• Approximately 10-16% of DCIS cases may have negative or minimal mammographic findings, emphasizing the importance of clinical correlation 1
• Magnification views are essential for proper characterization of calcifications and should be obtained routinely when microcalcifications are detected 1
• Mammography may underestimate the extent of disease, particularly in DCIS, by up to 2 cm in 50% of cases when only standard two-view mammography is performed 1

Imaging Sensitivity Considerations

• Mammography has 92-100% sensitivity and 90-96% specificity for breast cancer detection overall 2
• For DCIS specifically, mammography is more sensitive (55%) than ultrasound (47%) due to superior visualization of microcalcifications 2
• Dense breast tissue can mask lesions, and additional imaging modalities (ultrasound, MRI) may be needed in high-risk patients with dense breasts 1, 2