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WHO Classification of Tumours
Fibroadenoma, NOS


Fibroadenomas constitute one of the two major categories of fibroepithelial tumours of the breast, the second being phyllodes tumours . Fibroepithelial breast tumours are biphasic lesions composed of an epithelial and a mesenchymal (stromal) component. The latter is quantitatively predominant and determines the overall appearance of the lesion.
Histologically, two different growth patterns are distinguished in fibroadenomas. In the pericanalicular pattern, stromal cells proliferate circumferentially around ducts. In the intracanalicular pattern, the ducts are compressed into clefts by the proliferating stromal cells. Occasionally, the mesenchymal component may show hypercellularity, atypical multinucleated giant cells, myxoid changes or hyalinization with dystrophic calcification, and in rare cases ossification. Mitoses are uncommon. The epithelial component may exhibit hyperplasia and metaplastic changes

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Berean K, Tron VA, Churg A, Clement PB (1986)
Mammary fibroadenoma with multinucleated stromal giant cells.
Am J Surg Pathol 10: 823-7

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Kuijper A, Mommers EC, van der Wall E, van Diest PJ (2001)
Histopathology of fibroadenoma of the breast.
Am J Clin Pathol 115: 736-42

. Fibroadenomas typically are painless, solitary, firm, mobile, slow-growing, well defined nodules measuring up to 3 cm. Multiple nodules and very large lesions (up to 20 cm) have been reported.
Fibroadenoma most frequently affects women of childbearing age. The majority of cases do not recur after complete excision. A slightly increased risk of developing cancer within fibroadenomas or following treatment has been reported

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Levi F, Randimbison L, Te VC, La Vecchia C (1994)
Incidence of breast cancer in women with fibroadenoma.
Int J Cancer 57: 681-3

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Dupont WD, Page DL, Parl FF, Vnencak-Jones CL, Plummer WD, Rados MS, Schuyler PA (1994)
Long-term risk of breast cancer in women with fibroadenoma.
N Engl J Med 331: 10-5

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Tavassoli FA, Devilee P (Eds.)
World Health Organization Classification of Tumours. Pathology and Genetics of Tumours of the Breast and Female Genital Organs.
3rd Edition
IARC Press: Lyon 2003