Atypical Ductal Hyperplasia (ADH)

Epidemiology:

Common sites:

Gross features:

Histologic features:

• proliferation of cells identical to DCIS, except:
• limited in extent of completely involved TDLU spaces
• <= 2mm, OR
• Less than two membrane-bound spaces
• monomorphic cell population admixed with a second population of non-uniform cells in the TDLU spaces, OR
• fail to completely fill ductal spaces
• rigid arches or bridges (without streaming architecture)
• must be low-grade nuclei
• lack nucleoli
• hyperchromatic

Immunophenotype:

Marker:	Sensitivity:	Specificity:
ER/PR (diffusely positive)	typically
HMWK (neg) (CK 5/6)

Molecular features:

Other features:

• Found in 5-17% of biopsies performed for calcifications
• Moderately increased risk of invasive breast cancer (3.0 to 5.0 relative risk, in either breast)

References:

• Lakhani SR, Ellis IO, Schnitt SJ, Tan PH, van de Vijver MJ. (eds) WHO Classification of Tumours of the Breast (2012)