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mammary fibroadenoma

Tuesday 18 January 2005

breast fibroadenoma, Benign cystosarcoma phyllodes, Cellular fibroadenoma, Cellular adenofibroma, Fetal fibroadenoma, Juvenile adenofibroma; mammary fibroadenoma

PO Webpathology BP

Definition : The mammary fibroadenoma is a benign mammary biphasic tumor with epithelial and stromal components.

It is a benign breast lesion that result from hyperplasia of the normal lobules.

It is a circumscribed, often large, breast mass usually occuring in adolescent females with stromal and epithelial hypercellularity but lacking the leaf-like growth pattern of phyllodes tumors.

Fibroadenoma is a benign tumor that arises from the epithelium and stroma of terminal duct-lobular unit. Grossly, the fibroadenomas are small, well-demarcated, firm, grayish-pink masses. The cut surface is bulging with a whorled appearance.

The median age at presentation for fibroadenomas is about 25 yrs. and the mean age is about 30 yrs.


- Benign phyllodes tumor of the breast, coexisting with fibroadenoma

Digital slides

- JRC:5213 : Intracanalicular mammary fibroadenoma.
- JRC:5214 : Intracanalicular mammary fibroadenoma.
- JRC:5215 : Giant mammary fibroadenoma.
- JRC:5217 : Giant mammary fibroadenoma.
- JRC:5220 : Mammary fibroadenoma.
- Flickr


- fibroadenoma, intercanalicular type
- fibroadenoma, intracanalicular type


- Common
- Benign
- Usually aged 20–35 years
- Multiple in 20%: in same breast or bilaterally
- Increase in size during pregnancy
- Tend to regress as patient ages


- Appears to be benign neoplasm of specialized stroma of breast with accompanying epithelial component
- Rapidly growing fibroadenomas in immunosuppressed individuals contain Epstein–Barr virus
- No differences between fibroadenomas removed from patients taking oral contraceptives and those in controls except occasional formation of acini in former


Grossly, the fibroadenomas are small, well-demarcated, firm, grayish-pink masses. The cut surface is bulging with a whorled appearance. The cut surface of fibroadenoma may show slit-like spaces (as seen here). Necrosis is usually absent. The cut surface has multi-lobulated appearance.

- sharply demarcated
- firm
- @<@3 cm diameter
- Cut surface: solid, grayish white, bulging
- whorl-like pattern
- slit-like spaces
- No necrosis


- Appearance varies and depends on: relative amount and configuration of glandular tissue ans relative amount of connective tissue

  • intracanalicular (a misnomer) when connective tissue invaginates into glandular spaces and appears to be within them
  • pericanalicular when regular glandular configuration of glands maintained

- often both types in same lesion
- distinction has no practical connotations
- slightly hypercellular stroma but not to a degree that would justify a diagnosis of phylloides tumor.

- Tubule cells:

  • cuboidal or low columnar
  • round uniform nuclei
  • rest on myoepithelial cell layer

- Stroma:

  • usually loose connective tissue rich in acid mucopolysaccharides
  • may be partially or totally dense fibrous type

- spindle cells:

  • predominantly CD34-positive fibroblasts
  • admixed with scattered FXIIIa-positive dendrophages

- no elastic tissue
- consistent with presumed terminal duct–lobular unit (TDLU) origin of lesion

- cellularity varies from case to case:

  • if unduly hypercellular consider alternative diagnosis phylloides tumor

The histologic appearance of fibroadenoma depends upon the relative proportions and the arrangement of glandular and stromal components.

When the stromal connective tissue invaginates into the glandular component, it is labeled intracanalicular pattern. The compressed ducts show linear branching pattern with slit-like lumens (very well seen here). The stromal connective tissue invaginates into the glandular epithelium and appears to be contained within it.

In pericanalicular histologic pattern, the glands maintain their round or oval profiles. There is no prognostic or clinical significance attached to the pericanalicular and intracanalicular patterns. Both may be seen within the same lesion. The tubules and glands in a fibroadenoma are lined by cuboidal or low columnar epithelium with uniform nuclei and surrounded by a myoepithelial layer. The stroma is made up of loose connective tissue. If the stroma is hypercellular, the diagnosis of phyllodes tumor should be excluded.

In some cases, epithelial hyperplasia can be marked. It tends to occur more commonly in juvenile fibroadenomas.

There is a distinct variant of fibroadenoma that is large, hypercellular, and tends to occur in young adolescents, Juvenile Fibroadenoma. They occur more often in African-Americans and may be bilateral. High power view shows proliferation of glandular and stromal elements in a pericanicular growth pattern.There is mild epithelial hyperplasia and stromal hypercellularity. The epithelial hyperplasia is of no significance unless it has sufficient atypia to merit consideration for the diagnosis of carcinoma. Juvenile fibroadenoma have been referred to by a variety of names, as giant fibroadenoma, cellular fibroadenoma etc.

Malignant transformation is seen in 0.1% of cases of fibroadenomas. It usually involves the epithelial component. About 95% of cases are in-situ lesions. In rare cases of malignancy arising in a fibroadenoma, sarcomatous transformation may be seen.

Special Stains and Immunohistochemistry

- progesterone receptors: almost universal
- estrogen receptors: ≈25% of cases


If multiple and highly myxoid may be component of Carney complex, which includes:
- endocrine hyperactivity
- cardiac myxoma
- cutaneous hyperpigmentation
- other abnormalities
- other breast abnormalities:
- lobular and nodular myxoid changes
- ductal adenoma with tubular features

Differential Diagnosis

- mammary phylloides tumor

  • The mammary fibroadenoma has a slightly hypercellular stroma but not to a degree that would justify a diagnosis of phylloides tumor.
    - mammary tubular adenoma
    - mammary adenomyoepithelioma


- ≈20% have clonal chromosome aberrations in stromal component


- Low long-term risk for breast carcinoma: increased risk if:

  • complex
  • ductal hyperplasia
  • family history of breast carcinoma

- not increased risk if foci of atypical epithelial hyperplasia

- Malignant changes in 0.1% of cases:

  • usually epithelial component
  • most in situ (low-grade intraductal carcinoma)
  • +/- entirely within confines of fibroadenoma
  • +/- involves surrounding breast
  • +/- may represent extension into fibroadenoma by carcinoma
  • +/- originating elsewhere in breast

- sarcomatous transformation of stroma even rarer

Differential diagnosis: mammary biphasic lesions

- adenomyoepithelioma
- mammary fibroadenomas

  • mammary juvenile fibroadenoma

- mammary hamartoma
- metaplastic mammary carcinoma
- phyllodes tumor
- pleomorphic adenoma
- gynecomastia
- pubertal macromastia

See also

- fibroadenomatosis
- mammary tumors




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