Fibroadenoma
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Fibroadenoma is a common benign (non-cancerous) breast lump made of glandular and connective tissue. It is especially common in adolescents and younger adults.
Typical features
- Smooth, round or oval, well-defined lump
- Firm or rubbery, often described as “marble-like”
- Usually moves freely under the skin
- Often painless
- May become larger in pregnancy and shrink after menopause
Diagnosis
A clinician evaluates any new breast lump with examination and usually imaging, commonly ultrasound in younger people. A core needle biopsy may be needed when imaging or examination is not clearly typical, when the lump is enlarging, or when there are concerning features.
Treatment
Most confirmed, small, stable fibroadenomas can be observed with clinical or imaging follow-up. Removal or another procedure may be considered if it:
- Is growing rapidly or is large, often over about 5 cm
- Causes pain, anxiety, or cosmetic distortion
- Has uncertain biopsy/imaging findings
- Could represent a related lesion such as a phyllodes tumor
Surgical excision is common when treatment is needed. In selected small, biopsy-confirmed lesions, cryoablation may be an option. American Cancer Society guidance
Cancer risk
A typical simple fibroadenoma has little to no meaningful increase in breast-cancer risk. “Complex” fibroadenomas may be associated with a small increase in risk and should be interpreted with the rest of the pathology and personal/family risk factors. Berek & Novak's Gynecology, p. 1730.
Seek prompt medical assessment if
- A breast lump is new
- It is rapidly enlarging, hard/fixed, irregular, or persistent
- There is nipple discharge, skin dimpling, nipple inversion, redness, or enlarged underarm nodes
A recent systematic review also discusses management of multiple fibroadenomas (PMID 41919577); another recent review assessed cryoablation (PMID 41061430).
Pathology
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Fibroadenoma: Pathology
Definition
A fibroadenoma is a benign, biphasic fibroepithelial tumour of the breast arising from the terminal duct-lobular unit. It contains both:
- Epithelial component: benign ducts and lobules
- Stromal component: specialized fibrous intralobular stroma
It is the most common benign breast tumour in adolescents and young women. Pathology Outlines review
Gross pathology
- Usually a solitary, round or oval, well-circumscribed mass
- Often 1 to 3 cm, but can be larger
- Firm, rubbery, mobile
- Cut surface: homogeneous, pale grey-white, bulging or whorled
- Typically lacks hemorrhage, necrosis, and infiltrative margins
- It is sharply circumscribed but not necessarily truly encapsulated.
Microscopy
Fibroadenoma is a biphasic lesion composed of bland epithelial and stromal elements.
Epithelial component
- Benign ducts lined by:
- Inner luminal epithelial cells
- Preserved outer myoepithelial cell layer
- May show usual ductal hyperplasia, apocrine metaplasia, cystic change, or calcification.
- No epithelial atypia or invasive growth in a usual fibroadenoma.
Stromal component
- Fibrous or variably cellular stroma surrounds and distorts ducts.
- Stromal cellularity is generally uniform throughout the lesion.
- Stromal cells are bland, without marked atypia, stromal overgrowth, necrosis, or significant mitotic activity.
Histological patterns
Both patterns may occur within the same tumour and do not by themselves change prognosis.
| Pattern | Microscopic appearance |
|---|---|
| Pericanalicular | Stroma surrounds round/open ducts, which retain relatively open lumina. |
| Intracanalicular | Proliferating stroma compresses ducts into elongated, slit-like, branching spaces. |
In S. Das A Manual on Clinical Surgery, pericanalicular fibroadenoma is described as having fibrous tissue around tubular glands, while intracanalicular fibroadenoma has compressed and distorted, spidery glandular spaces.
Variants
- Juvenile fibroadenoma: occurs mainly in adolescents, often larger and more cellular, but remains benign.
- Giant fibroadenoma: conventionally larger than 5 cm; may produce marked breast asymmetry.
- Complex fibroadenoma: fibroadenoma containing one or more of apocrine cysts, sclerosing adenosis, epithelial calcifications, or papillary apocrine change.
- Myxoid fibroadenoma: has abundant myxoid stroma; can be associated with Carney complex.
Differential diagnosis: fibroadenoma versus phyllodes tumour
| Feature | Fibroadenoma | Phyllodes tumour |
|---|---|---|
| Margins | Circumscribed | May be more irregular/infiltrative |
| Stromal cellularity | Usually uniform, mild to moderate | Often increased and heterogeneous |
| Architecture | No characteristic leaf-like pattern | Leaf-like architecture with epithelial-lined clefts |
| Periductal stroma | No marked condensation | Subepithelial/periductal stromal condensation may occur |
| Stromal atypia/mitoses | Usually absent or minimal | May be increased, especially in borderline/malignant lesions |
| Stromal overgrowth | Absent | May be present |
| Clinical course | Benign | Can recur; borderline/malignant forms can metastasize |
The distinction can be difficult on core biopsy, particularly for a highly cellular fibroadenoma with prominent intracanalicular architecture. A recent pathology review specifically addresses this diagnostic overlap (PMID 41979873).
Key exam summary
Fibroadenoma is a benign, well-circumscribed biphasic breast tumour composed of benign ducts and uniform fibrous stroma. Microscopically it displays pericanalicular and/or intracanalicular growth patterns, without significant stromal atypia, stromal overgrowth, or leaf-like architecture.
Fibroadenomas may regress, remain stable, or grow, particularly with hormonal influence. Berek & Novak's Gynecology, p. 1730.
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