Histology Course A IV 26 Department of Pathology, University of Zurich Histokurs

A IV 26

fibroadenoma of the breast HE further information (German) on HiPaKu 
  ICD-10: C50.9; ICD-O: 9010/0
36-year-old female noticed a lump in one breast.
- Circumscribed tumor demarcated from the normal mammary tissue by a fibrous capsule.
- The loose stroma contains fibroblasts and collagen fibers. In the stroma inclusion of duct-like epithelial structures of various forms and sizes. In part, regular, open, round to oval ducts. Some ducts are compressed by proliferating stroma. These ducts appear on cross-sections as slits or irregular star-like structures.
- Usually, two cell layers can be distinguished within the ducts an inner epithelial and an outer myoepithelial layer. The latter faces the well-defined, intact basement membrane.

Differential diagnosis:
Phyllodes tumor: Typically, leaf-like slits and clefts are observed. The stroma exhibits an increased cellularity. In malignant variants, a high mitotic activity and anaplastic cells are observed in the stroma.