Mammary Hamartoma

Definition

• Sharply circumscribed breast mass composed of normal or fibrocystic appearing tissue

Alternate/Historical Names

• Adenolipoma (variant)
• Choristoma
• Fibroadenolipoma
• Muscular or myoid hamartoma (variant)

Diagnostic Criteria

• 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

Original posting:: May 15, 2006

Supplemental studies

Immunohistology

• Actin, calponin, p63
• Highlight myoepithelial cells with normal distribution
• Actin may demonstrate smooth muscle cells in myoid hamartoma
• CD34 may stain areas of PASH
• CD34 reported to stain muscle cells of myoid hamaratoma

Differential Diagnosis

• Non-specific fibrocystic disease
• Adenomyoepithelioma
• Cowden disease
• Fibroadenoma
• Diabetic mastopathy
• Intramammary lipoma
• Gynecomastia-like lesion of the female breast

Nonspecific fibrocystic disease

• Mammary hamartoma is distinguished only based on its circumscription and formation of a discrete mass

Adenomyoepithelioma	Myoid Hamartoma
Myoepithelial component positive for keratin, p63, smooth muscle actin	Myoid component positive only for smooth muscle actin
Tubules without lobules	Well formed ducts and lobules
No admixed fat	Admixed fat

Cowden disease

• May be indistinguishable if circumscribed and solitary
• Diffuse or bilateral lesions favor Cowden disease

Fibroadenoma	Mammary Hamartoma
Lobules infrequent	Lobules typically present (may be atrophic)
Frequent intracanalicular or tubular glandular proliferation	Morphologically normal ducts and lobules
Intralesional fat rare	Fat integral to lesion

Diabetic Mastopathy / Lymphocytic Mastitis	Mammary Hamartoma
Epithelioid stromal cells	No epithelioid stromal cells
Prominent B cell infiltrates	No significant B cell infiltrates

Both have keloidal fibrosis

Intramammary lipoma vs Adenolipoma

• Ducts and lobules prominent in adenolipoma
• Ducts and lobules rare or absent in lipoma
• No clinical significance to the distinction

Mammary Hamartoma	Gynecomastia-like Lesion of the Female Breast
Circumscribed	Not circumscribed
Contains lobules	No lobules
No periductal stromal changes	Periductal stromal fibrosis or edema
May contain stromal smooth muscle or cartilage	No stromal smooth muscle or cartilage

Clinical

• Rare lesion, <1% of breast biopsies
• Age range 18-89 but most premenopausal
• Unilateral
• Benign, infrequent recurrences reported
  • No special clinical significance to recognition of myoid or adenolipomatous variants
• One male case of myoid hamartoma reported
• One ectopic (inguinal) case reported
• Nearly always a palpable or radiographically distinct mass

Lists

Breast Tumors and Lesions Exhibiting Reactivity for Muscle/Myoepithelial Markers

(Most benign lesions with an epithelial component will have a myoepithelial cell layer)

• Adenoid cystic carcinoma
• Adenomyoepithelioma
• Apocrine adenoma
• Apocrine adenosis
• Ductal Adenoma
• Infiltrating syringomatous adenoma
• Juvenile papillomatosis
• Low grade adenosquamous carcinoma
• Metaplastic carcinoma
• Myoepithelial carcinoma
• Myoepithelioma
• Myofibroblastoma
• Myoid hamartoma
• Pleomorphic adenoma
• Pseudoangiomatous stromal hyperplasia (cellular lesions)

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