Atypical Ductal Hyperplasia of the Breast

Definition

A proliferative ductal lesion that demonstrates some but not all features of low or intermediate grade ductal carcinoma in situ

Low Grade DCIS and Intermediate Grade DCIS require cytologic, architectural and size criteria to be met
Atypical ductal hyperplasia is a term applied to proliferative ductal lesions with any one of the following sets of features:
- Ducts completely filled and exhibit sharp punched out spaces or micropapillae but lack uniform cytologic features
  - Presence of even a partial population of columnar cells, or
  - Presence of even focal streaming of cells
- OR: Ducts filled by a uniform population of cells with cytologic features of low grade DCIS but lack architectural features
  - Only partial filling of ducts, or
  - Lack of uniformly sharp punched out spaces, microacini or characteristic micropapillae
    - Solid low grade DCIS is rare but must be excluded before using this feature to diagnose ADH
- OR: Cytologic and architectural features met but failure to meet size criteria
  - Fewer than two duct spaces involved or less than 2-3 mm in aggregate dimension
High grade cytology excludes a lesion from consideration for atypical ductal hyperplasia, regardless of architecture or size