Tumours of the intralobular stroma: fibroadenoma vs phyllodes tumour
- Lesion
Both tumours grow from the stroma around the lobules. Fibroadenoma is the harmless lump of young women; phyllodes is larger, older and can recur or spread.
What it is
Fibroadenoma and phyllodes tumour are biphasic tumours in which the specialised stroma of the lobule proliferates and carries ducts along with it. Fibroadenoma is the commonest benign breast tumour, typical of young women: a mobile, rubbery, well-circumscribed lump that often carries MED12 mutations. Phyllodes tumour occurs a decade or more later, grows larger and faster, and has a more cellular stroma that pushes leaf-like fronds into cleft-like spaces. Phyllodes tumours are graded benign, borderline or malignant; they tend to recur locally, and malignant ones can spread through the blood.
Structure
- Fibroadenoma: stroma surrounding ducts (pericanalicular) or pressing them into curved slits (intracanalicular), both with a two-layered epithelium.
- Phyllodes: club-like fronds of cellular stroma covered by epithelium, projecting into elongated spaces; stromal cells condense beneath the epithelium.
- Malignant phyllodes: stroma with marked atypia, many mitoses, overgrowth without epithelium and infiltrative borders; heterologous sarcoma may appear.
Step by step
- A stromal cell of the lobule acquires a MED12 mutation.
- The clone proliferates under hormonal influence and drags ducts into the growing tumour (fibroadenoma).
- In phyllodes tumours, additional changes (TERT promoter and others in higher grades) make the stroma more cellular and autonomous.
- Malignant phyllodes stroma behaves like a sarcoma and can reach the lungs and bone through the blood.
Fibroadenoma vs phyllodes tumour
| Feature | Fibroadenoma | Phyllodes tumour |
|---|---|---|
| Typical age | Twenties and thirties | Forties to sixties |
| Size and growth | Usually small, slow | Often large, can grow rapidly |
| Architecture | Slit-like ducts in uniform stroma | Leaf-like fronds into cleft-like spaces |
| Stroma | Low cellularity, no atypia | Increased cellularity, atypia and mitoses vary with grade |
| Behaviour | Benign, rarely recurs | Local recurrence; malignant ones metastasise by blood |
| Treatment | Observation or simple excision | Excision with a clear margin |
Markers
- CD34 and ER-beta in stroma (variable)
- Ki-67 (higher in phyllodes)
- MED12 and TERT promoter testing (research and difficult cases)
Clinical notes
- A young woman with a mobile, painless, rubbery lump most likely has a fibroadenoma; imaging and a core biopsy confirm it.
- A rapidly growing fibroepithelial lump in an older woman suggests phyllodes tumour and needs wide excision.
- Multiple fibroadenomas can occur in women taking cyclosporine after transplantation.
Test yourself
Think of the answer, then tap the question to see it.
What is the most common benign breast tumour in young women?
Fibroadenoma.
How does a phyllodes tumour differ from a fibroadenoma under the microscope?
It has more cellular stroma with overgrowth and leaf-like fronds projecting into cleft-like spaces; atypia and mitoses increase with grade.
Why is axillary dissection not done for malignant phyllodes tumour?
Its malignant stroma spreads by blood like a sarcoma, rarely to lymph nodes.
Elsewhere in DurgiPedia
Connections
Educational content on the mechanisms of disease; not a diagnostic or treatment guide and no substitute for a health professional's advice. No doses are given.
Sources: Fibrocystic Breast Disease (StatPearls (NCBI Bookshelf), 2026); Breast Cancer Treatment (PDQ®)–Health Professional Version (National Cancer Institute, 2026).
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Representative model, for educational purposes only.