What does a BI-RADS (Breast Imaging-Reporting and Data System) category of 4 or higher indicate?

BI-RADS Category 4 or Higher: Suspicious Abnormalities Requiring Biopsy

BI-RADS category 4 or higher indicates suspicious breast lesions that warrant biopsy due to a significant risk of malignancy, with BI-RADS 4 having a malignancy risk ranging from >2% to <95% and BI-RADS 5 having a malignancy risk of ≥95%. 1

BI-RADS Classification System Overview

The Breast Imaging-Reporting and Data System (BI-RADS) is a standardized classification system developed by the American College of Radiology (ACR) to report breast imaging findings. The system includes the following categories relevant to suspicious findings:

• BI-RADS 4: Suspicious abnormality where biopsy should be considered. These lesions have a wide probability range of malignancy (>2% to <95%) 1
• BI-RADS 5: Highly suggestive of malignancy with ≥95% probability of cancer 1
• BI-RADS 6: Known biopsy-proven malignancy before definitive therapy 1

BI-RADS 4 Subcategories

BI-RADS 4 is further divided into three subcategories based on the level of suspicion:

• BI-RADS 4A: Low suspicion for malignancy (>2% to ≤10% risk)

  • Positive predictive value of approximately 19.5% 2
  • Only about 10% of these lesions are ductal carcinoma in situ (DCIS) 3

• BI-RADS 4B: Intermediate suspicion for malignancy (>10% to ≤50% risk)

  • Positive predictive value of approximately 41.5% 2
  • About 21% of these lesions are DCIS 3

• BI-RADS 4C: Moderate concern, but not classic for malignancy (>50% to <95% risk)

  • Positive predictive value of approximately 74.3% 2
  • About 70% of these lesions are DCIS 3

Clinical Implications and Management

Biopsy Recommendations

• All BI-RADS 4 lesions require tissue diagnosis, typically through image-guided core needle biopsy 4
• Even for BI-RADS 4A lesions with lower suspicion, biopsy is still recommended over follow-up 4
• For palpable lesions categorized as BI-RADS 3 or higher, the American College of Radiology recommends biopsy, especially if new, enlarging, or in high-risk patients 4

Specific Features Associated with Malignancy

Imaging features strongly associated with malignancy in BI-RADS 4 lesions include:

• Irregular shape (PPV 66%) 2
• Spiculated margin (PPV 80%) 2
• Nonparallel orientation (PPV 58.9%) 2
• Age ≥50 years (OR 8.99) 5
• Non-circumscribed indistinct margin (OR 4.05) 5
• Microlobulated margin (OR 2.95) 5
• Presence of calcifications (OR 2.64) 5

Role of Additional Imaging

• MRI can be helpful in further characterizing BI-RADS 4 lesions detected on mammography or ultrasound
  • Can potentially avoid 92% of unnecessary biopsies for certain BI-RADS 4 lesions 6
  • Has a 0% false-negative rate for all ultrasound findings and for mammographic findings except pure clustered microcalcifications 6
  • However, MRI should not replace biopsy as the primary management for BI-RADS 4 lesions 4, 7

Important Considerations

• The final BI-RADS assessment category is based on the most worrisome findings when multiple imaging modalities are used 1
• Patient anxiety or request for removal should be considered when deciding on tissue sampling or surgical excision 4
• For complex cystic lesions, which have a relatively high risk of malignancy, tissue diagnosis is required to exclude malignancy 4

Follow-Up After Biopsy

• If biopsy results are malignant, proceed with definitive surgical management 4
• If biopsy reveals atypia, surgical excision is recommended 4
• If biopsy results are benign and concordant with imaging, follow-up imaging at 6-12 months is recommended 4

Remember that while BI-RADS 4 encompasses a wide range of malignancy probability, the primary management recommendation remains the same: tissue diagnosis through biopsy to determine if cancer is present.