Microglandular Adenosis

Microglandular adenosis (MGA) of the breast may be difficult to separate from well differentiated invasive ductal carcinoma and invasive tubular carcinoma.
A panel of IHC stains is useful in the differential, including S-100 (positive only with MGA) ER, PR, HER2, and EMA (positive only in well differentiated invasive ductal carcinoma and invasive tubular carcinoma). (ref: Arch Pathol Lab Med, vol 144 Jan 2020, 42-46)