mammary fibroadenoma - Humpath.com - Human pathology - Photos - pictures

Definition: Benign breast lesion that result from hyperplasia of the normal lobules. 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.

Synopsis

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

Pathogenesis

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

Gross Pathology

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

Histopathology

Appearance varies and depends on: relative amount and configuration of glandular tissue; relative amount of connective tissue
slightly hypercellular stroma but not to a degree that would justify a diagnosis of phylloides tumor.
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

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 dendrophages4,5
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

Special Stains and Immunohistochemistry

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

Predisposition

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 changes26
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

Genetics

≈20% have clonal chromosome aberrations in stromal component

Prognosis

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