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  • Surgical Pathology Criteria

    Mammary Hamartoma


    • 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


    • 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

    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


    • 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


    Breast Tumors and Lesions Exhibiting Reactivity for Muscle/Myoepithelial Markers

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


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