Microglandular adenosis of the female breast is benign but can be easily confused with tubular carcinoma.


Appearance on hematoxylin and eosin stains:

(1) disorganized proliferation of small tubular glands with a single epithelial cell layer

(2) infiltrative growth pattern with extension into fat

(3) absence of a tubulocentric configuration

(4) typical absence of a myoepithelial cell layer

(5) absence of elastosis in the stroma


Immunohistochemical features:

(1) calponin, p63, and smooth muscle actin negative (lack of myoepithelial cell layer)

(2) S-100 strongly positive

(3) EMA negative

(4) negative for ER, PR and HER2 ("triple negative")

(5) collagen IV stains an intact circumferential basement membrane


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