Mammary Hamartoma

Definition

Sharply circumscribed breast mass composed of normal or fibrocystic appearing tissue

Sharply circumscribed mass
- Nearly always palpable or radiographically distinct
Composed of fibrous, fatty and glandular tissue
- Fibrous tissue may be dense and keloid-like
- Well formed ducts and lobules witih epithelial and myoepithelial cells
  - Ducts may be cystic
  - Lobules may be atrophic
  - Normall peripheral distribution of myoepithelial cells
- Fat cells admixed
  - If fat is predominant, lesion may be termed Adenolipoma
    - No special clinical significance
- Appearance may be indistinguishable from fibrocystic change
  - Circumscription is the only difference
- Cells with smooth muscle differentiation may be seen
  - When smooth muscle cells are prominent, such lesions have been termed Myoid Hamartomas
    - Smooth muscle cells may be spindled or epithelioid
    - No special clinical significance
- Pseudoangiomatous stromal hyperplasia (PASH) has been reported in 25/35 mamary hamartomas
- Cartilage is rarely reported
  - May be considered metaplasia in a hamartoma
  - May be termed choristoma
- One report of brown fat
- Carcinoma has rarely been reported to involve mammary hamartomas
- Simlar findings have been reported in Cowden disease
  - May be indistinguishable if circumscribed and solitary
  - More common if diffuse or bilateral

Richard L Kempson MD
Robert V Rouse MD
Department of Pathology
Stanford University School of Medicine
Stanford CA 94305-5342