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Surgical Pathology Criteria

Fibroadenoma of the Breast


  • Circumscribed breast mass composed of benign stromal and epithelial cells

Alternate/Historical Names

  • Adult type fibroadenoma
  • Adenofibroma

Diagnostic Criteria

  • Circumscribed
    • May be multiple
  • Biphasic stromal and epithelial process
    • Intracanalicular pattern
      • Stroma compresses ducts into slit-like spaces
    • Pericanalicular pattern
      • Stroma surrounds round ducts
  • Bland, largely fibroblastic stroma
    • Myoepithelial cells and myofibroblasts not prominent
    • Hypocellular to variably hypercellular
    • Frequently myxoid
    • May be hyalinized, especially in older patients
    • May calcify
    • Rare stromal changes
      • Heterologous differentiation
        • Smooth muscle
        • Fat
        • Cartilage
        • Bone
      • Multinucleated giant cells
  • Ducts lined by epithelial and myoepithelial cells
    • Fibrocystic changes may be present
      • May be seen at least focally in half of cases
    • Areas typical of tubular adenoma may be present
      • Densely packed uniform round tubules
      • Termed "adenomatous transformation"
    • "Complex fibroadenoma" has been applied if any of the following are present
      • Cysts >3 mm diameter
      • Sclerosing adenosis
      • Epithelial calcifications
      • Papillary apocrine change
    • Atypical ductal or lobular hyperplasia may be present
    • Carcinoma, in situ or invasive, may be present
      • May be lobular or ductal
      • Identify using standard criteria
      • Invasive carcinoma is present in adjacent breast in half of patients with in situ carcinoma in a fibroadenoma
      • Mean age of cases with carcinoma is in 40's
  • Necrosis may be seen rarely
    • More frequent in pregnancy
  • Giant fibroadenoma
    • Tumors >500 g or disproportionally large compared to rest of breast
    • More frequent in young and black patients
    • We consider the term merely descriptive
    • May be either adult or juvenile type

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

Original posting:: May 27, 2006

Supplemental studies


  • Stromal cells
    • CD34, Factor XIIIa positive
    • Smooth muscle actin typically negative to focal/weak

Differential Diagnosis

(Adult Type) Fibroadenoma Juvenile Fibroadenoma
Hypocellular to variably cellular stroma Uniformly hypercellular stroma


Fibroadenoma Low Grade Phyllodes Tumor
Lacks significant stromal hypercellularity Hypercellular stroma is prominent
No stromal overgrowth May have stromal overgrowth
No leaf-like architecture Prominent leaf-like architecture
No condensation around ducts Stromal condensation around ducts
Does not infiltrate May infiltrate surrounding breast
The histologic border between these two is not always sharp


Fibroadenoma High Grade Phyllodes Tumor
Lacks significant stromal hypercellularity Hypercellular stroma
No stromal overgrowth Stromal overgrowth
No stromal atypia Pleomorphic stromal cells
Stromal mitotic rate < 3/hpf Elevated stromal mitotic rate, usually >4-5 per 10 hpf, abnormal forms may be found
Does not infiltrate May infiltrate surrounding breast
Stromal overgrowth defined as at least one low power field (40x total magnification) composed entirely of stroma


Adenomatous Transformation of Fibroadenoma Tubular Adenoma
Areas of typical fibroadenoma stroma Scant stroma
Variable tubules Uniform tubules
Areas typical of tubular adenoma may be found within fibroadenomas


Fibroadenoma Fibrocystic Disease
Discrete, circumscribed lesion May contain poorly circumscribed areas of fibrocystic change


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


  • Peak age in twenties
    • Uncommon after menopause
      • Frequently smaller and hyalinized
  • Multiple in 25% of patients

Relative risk for development of invasive breast carcinoma

  • No increased risk
    • Non-proliferative fibrocystic change
    • Fibroadenoma
    • Solitary papilloma
  • Slightly increased risk (1.5 to 2 times)
    • Proliferative fibrocystic change
    • Usual ductal hyperplasia
    • Sclerosing adenosis (florid)
    • Radial scar
    • Complex fibroadenoma (approximately 3 times risk)
  • Moderately increased risk (4 to 5 times)
    • Atypical ductal hyperplasia (no family history)
    • Atypical lobular hyperplasia
  • High risk (8 to 10 times)
    • Ductal carcinoma in situ, low grade
    • Lobular carcinoma in situ
    • Atypical ductal hyperplasia, if history of carcinoma in primary relatives
  • Very high risk (precise level not known)
    • Ductal carcinoma in situ, high grade

Grading / Staging / Report

Grading / Staging

  • Not applicable


Biphasic lesions of the breast


  • Rosen PP, Oberman HA. Tumors of the Mammary Gland, Atlas of Tumor Pathology, AFIP Third Series, Fascicle 7, 1993
  • Lerwill MF. Biphasic lesions of the breast. Semin Diagn Pathol. 2004 Feb;21(1):48-56.
  • Dehner LP, Hill DA, Deschryver K. Pathology of the breast in children, adolescents, and young adults. Semin Diagn Pathol. 1999 Aug;16(3):235-47.
  • Powell CM, Cranor ML, Rosen PP. Multinucleated stromal giant cells in mammary fibroepithelial neoplasms. A study of 11 patients. Arch Pathol Lab Med. 1994 Sep;118(9):912-6.
  • Musio F, Mozingo D, Otchy DP. Multiple, giant fibroadenoma. Am Surg. 1991 Jul;57(7):438-41.
  • Raganoonan C, Fairbairn JK, Williams S, Hughes LE. Giant breast tumours of adolescence. Aust N Z J Surg. 1987 Apr;57(4):243-7.
  • Dupont WD, Page DL, Parl FF, Vnencak-Jones CL, Plummer WD Jr, Rados MS, Schuyler PA. Long-term risk of breast cancer in women with fibroadenoma. N Engl J Med. 1994 Jul 7;331(1):10-5.
  • Silverman JS, Tamsen A. Mammary fibroadenoma and some phyllodes tumour stroma are composed of CD34+ fibroblasts and factor XIIIa+ dendrophages. Histopathology. 1996 Nov;29(5):411-9.
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