What are the main signs of breast cancer on a mammogram?

Main Mammographic Signs of Breast Cancer

The most important mammographic signs of breast cancer are microcalcifications (present in 62% of malignancies), spiculated masses, and architectural distortion, with calcifications being particularly critical as they represent the primary finding in the majority of ductal carcinoma in situ cases. 1, 2

Primary Malignant Features

Microcalcifications

• Calcifications are the single most common mammographic finding of malignancy, detected in 62% of breast cancer cases 1
• Pleomorphic microcalcifications carry a ≥95% probability of malignancy when clustered or grouped 2
• Fine linear or fine-linear branching calcifications are characteristic of high-grade DCIS with necrosis 2
• The distribution pattern matters significantly: irregular or triangular clusters suggesting segmental or ductal distribution are more concerning than round or oval patterns 1, 2
• Calcifications are present in approximately 80-90% of DCIS cases, making them the hallmark finding for this cancer type 2

Masses

• Spiculated masses are the classic appearance of invasive breast cancer, presenting as irregular densities with radiating lines extending from the margins 2, 3
• Poorly defined nodules are highly suspicious for malignancy 3
• Even circumscribed masses can represent cancer in a small percentage of cases, though most are benign 4

Architectural Distortion

• Architectural distortion without an associated mass is a critical finding that carries a 2.21-fold increased risk of subsequent breast cancer compared to masses alone 5
• This finding can be extremely subtle and requires optimal technique and meticulous interpretation 4
• Architectural distortion was present in 16.7% of posterior breast cancers 6

Secondary Suspicious Features

Asymmetries and Soft Tissue Changes

• Focal asymmetric density was found in 12.6% of posterior breast cancers 6
• Soft tissue changes other than calcifications were present in 22% of DCIS cases 1
• Focal asymmetry requires further evaluation as it can represent underlying malignancy 2

Less Common Findings

• Nodules or prominent ducts (8% of DCIS cases) 1
• Multiple findings on mammography carry a 1.89-fold increased risk of subsequent breast cancer 5
• Skin thickening with trabecular distortion can indicate inflammatory breast cancer 2

Critical Clinical Pitfalls to Avoid

Negative Mammograms Do Not Exclude Cancer

• Approximately 10-16% of DCIS cases have negative or minimal mammographic findings 1, 2
• Never allow negative imaging to override a clinically suspicious palpable mass 2
• Mammography has 92-100% sensitivity overall, but this means 0-8% of cancers can be missed 2

Technical Considerations

• Magnification views are essential and should be obtained routinely when microcalcifications are detected to properly characterize their shape, number, and extent 1, 2
• Standard two-view mammography alone can underestimate DCIS extent by 2 cm in up to 50% of cases 1
• Additional specialized views (spot compression, magnification) are necessary to complete the evaluation 1, 3

Specific Cancer Type Considerations

• Invasive lobular carcinoma often presents with subtle findings: architectural distortion and focal asymmetric density rather than obvious masses 6
• For DCIS specifically, mammography (55% sensitivity) is more sensitive than ultrasound (47% sensitivity) due to superior visualization of microcalcifications 2
• Dense breast tissue can mask lesions, requiring additional imaging modalities (ultrasound, MRI) in high-risk patients 2

BI-RADS Risk Stratification Framework

• BI-RADS 5 indicates ≥95% probability of cancer: includes spiculated masses and malignant-appearing pleomorphic calcifications 2
• BI-RADS 4 indicates suspicious findings with 2-95% malignancy probability: biopsy should be considered 2
• In one study, 87.5% of posterior breast cancers were classified as BI-RADS 4 or 5 on standard two-view mammography, increasing to 100% after additional views 6