Fibroadenoma Composition
A fibroadenoma is a benign breast tumor composed of both stromal (connective tissue) and epithelial (glandular) elements 1.
Tissue Components
The fibroadenoma consists of two distinct tissue types that proliferate together:
- Stromal component: Connective tissue framework that forms the bulk of the tumor
- Epithelial component: Glandular tissue derived from the terminal ductal lobular unit 2
This dual composition distinguishes fibroadenomas as fibroepithelial tumors 3. The proliferation involves both the epithelial cells lining the ducts and the surrounding stromal (connective) tissue, originating specifically from the terminal ductal unit of the breast 2.
Clinical Significance of Composition
The epithelial component can exhibit various changes including:
- Hyperplasia (found in 32.3% of cases) 4
- Hormone-responsive features with estrogen-sensitive signatures 5
- Rarely, atypical changes or carcinoma in situ (2.0% of cases) 4
Important caveat: While the epithelial component may occasionally harbor proliferative changes or atypia, the fibroadenoma itself remains a benign entity. The stromal component is what primarily distinguishes it from purely epithelial lesions.
The balanced proliferation of both tissue types is what creates the characteristic appearance on imaging and histology, though distinguishing cellular fibroadenomas from phyllodes tumors (which also contain stromal and epithelial elements) can be challenging 1, 3.