2. Atypical ductal hyperplasia “A diagnosis of ADH should not be made unless a diagnosis of low grade DCIS is being seriously considered” WHO Breast 2012 A matter of quantity Architecture: cribriform spaces, micropapillae (bulbous), rigid bars Cytology: ‘clonal’, monotonous, mild nuclear atypia, enlarged, nucleoli, distinct cell borders. Same as LG-DCIS

3. ADH/DCIS When does ADH become DCIS? A matter of quantity. Criteria still vary and are not standardized WHO states: > 2 mm and/or completely involving at least two duct spaces. Any intraductal proliferation with moderate-high grade nuclear features = DCIS (no size criteria). Sometimes ADH and UDH co-exist

4. IHC IHC : UDH vs ADH/DCIS  CK5/6 and ER  Caveat: Not helpful in columnar cell change or apocrine change.

5. Practical point If a core biopsy shows borderline features of ADH/DCIS, be conservative and call it ‘at least ADH’ An upgrade rate to DCIS on excision is well known and accepted. Harder to explain DCIS, limited to the core.

8. ER CK5/6