Atypical ductal hyperplasia

Definition

Monomorphic proliferation of epithelial cells filling <2 duct spaces or <2 mm in size (morphologically similar to low-grade DCIS but not full-fill cutoff criteria)

Significance

Highest upgrade rate to malignancy (approx. 15–30%) among B3 lesions (RR ~4-5x).

Management

• Surgical excision is the standard NCCN recommendation.
• Recent UK guidelines allow Vacuum Assisted Excision (VAE) if < 4mm and completely excised, but Surgery remains the "safe" exam answer for high-risk atypia.