What percentage of Breast Imaging-Reporting and Data System (BI-RADS) 4 lesions are malignant?

From the Guidelines

Approximately 20-30% of BI-RADS 4 breast lesions are malignant. The BI-RADS (Breast Imaging Reporting and Data System) category 4 indicates a suspicious abnormality that requires biopsy for definitive diagnosis. This category is further subdivided into 4A (low suspicion, 2-10% risk of malignancy), 4B (moderate suspicion, 10-50% risk of malignancy), and 4C (high suspicion, 50-95% risk of malignancy) 1. The wide range in malignancy rates reflects this subcategorization, with the overall average falling around 20-30%.

Key Points to Consider

• The BI-RADS category 4 lesions have an intermediate probability of cancer, ranging from 3% to 94% 1
• Tissue diagnosis using core needle biopsy or needle localization excisional biopsy with specimen radiograph is necessary for BI-RADS categories 4 and 5 lesions 1
• When a patient receives a BI-RADS 4 classification, a tissue biopsy is recommended regardless of which subcategory they fall into, as imaging alone cannot definitively determine whether the lesion is benign or malignant
• The biopsy results will guide further management decisions, which may include additional imaging, surgical excision, or cancer treatment if malignancy is confirmed

Management Recommendations

• For BI-RADS category 4 lesions, tissue diagnosis is necessary to determine the presence of malignancy
• Core needle biopsy is the preferred method for tissue diagnosis
• Concordance between the pathology report and the imaging finding must be obtained when a needle biopsy is performed 1

From the Research

BI-RADS 4 Lesions Malignancy Percentage

• The percentage of Breast Imaging-Reporting and Data System (BI-RADS) 4 lesions that are malignant varies across different studies, with reported rates including:
  • 38.7% malignant and 61.2% benign in a study of 186 BI-RADS 4 nonpalpable breast lesions 2
  • 17.8% of BI-RADS 4 lesions were malignant in a study of 429 lesions other than primary cancer initially assessed at preoperative MRI 3
• Subcategories of BI-RADS 4 lesions also have different malignancy rates, including:
  • 19.5% for subcategory 4A, 41.5% for subcategory 4B, and 74.3% for subcategory 4C in a study of 186 BI-RADS 4 nonpalpable breast lesions 2
  • 1.8% for subcategory 4A, 11.8% for subcategory 4B, and 67.5% for subcategory 4C in a study of 434 category 2-5 lesions on MRI 4

Factors Influencing Malignancy Rates

• The likelihood of malignancy in BI-RADS 4 lesions can be influenced by various factors, including:
  • Lesion characteristics, such as shape, margin, and echo pattern 2
  • The presence of other lesions, such as category 5 or 6 lesions 4
  • The use of structured integration of BI-RADS criteria, such as the Kaiser Score (KS) 5

Clinical Implications

• The management of BI-RADS 4 lesions depends on various factors, including the likelihood of malignancy and the presence of other lesions 3
• Annual follow-up may be adequate for preoperative MRI-detected BI-RADS 3 lesions and BI-RADS 4 lesions followed up after benign-concordant biopsy 3