Fibroadenoma: features and behaviour
A fibroadenoma is a benign breast tumour in which supporting tissue and gland cells overgrow together, typically a smooth lump that slides under the fingers in a young woman.
Remember
A smooth, rubbery, sharply defined lump that slides under the fingers in a young woman is typically a fibroadenoma: benign, with very low malignant potential.
Memory aid
the breast mouse is smooth, rubbery and slippery
Picture the breast mouse sliding away under the fingers when you feel the lump.
A fibroadenoma is the most common benign breast tumour and usually appears in women of reproductive age. The name tells you what it is made of: fibro (fibrous stroma), adeno (gland) and -oma (a lump). Stroma is the supporting connective tissue, and the gland cells are epithelial cells, so the tumour is a proliferation (overgrowth) of both together. Pathologists call a tumour built from both fibroepithelial.
The two tissues grow together without invading the tissue around them, so the lump is smooth, round and rubbery, with a well-circumscribed (sharply defined) edge. It is usually painless and moves freely under the fingers, which is why it is nicknamed the breast mouse. On ultrasound it usually shows as a well-circumscribed oval with regular borders. When it is removed, it looks rubbery and grey-white.
A fibroadenoma has very low malignant potential: most stay the same or shrink, and removal is considered mainly if one is over 5 cm or suddenly grows. Even so, benign and malignant lumps overlap, so any new lump is still assessed by triple assessment: examination, imaging and needle biopsy.
The phyllodes tumour is the one to contrast. It is also fibroepithelial, but it is usually larger, is found in an older age group and can grow rapidly. About one third of phyllodes tumours have malignant potential.
Key facts
- Who
- Young women of reproductive age; fibroadenomas occur at any age, but more prominently under the age of 30.
- Feel
- Smooth and round, usually painless and highly mobile, so the lump slides under the fingers.
- Tissues
- A benign proliferation (overgrowth) of both stromal and epithelial tissue, so it is fibroepithelial.
- Ultrasound
- Usually a well-circumscribed (sharply defined) oval with regular borders.
- Behaviour
- It does not invade the surrounding breast or spread, and its malignant potential is very low.
- Removal
- Removal is considered mainly if one is over 5 cm or suddenly grows, and most are under 5 cm.
- Assessment
- Triple assessment (examination, imaging and needle biopsy), as for any new lump.
Exam traps
- A phyllodes tumour does not usually fit a lump in a young woman, because it is a rare fibroepithelial tumour that is usually larger, is found in an older age group and can grow rapidly.
- An overgrowth of the epithelium alone does not define a fibroadenoma, because a fibroadenoma needs both epithelial and stromal elements.
- A breast lipoma can feel mobile, but it does not fit, because a lipoma is a soft benign tumour of fat and not stromal and epithelial tissue.
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