Your pathology report for fibroadenoma

by Jason Wasserman MD PhD FRCPC
October 3, 2025

A fibroadenoma is a benign (noncancerous) type of breast tumor. It is made of both epithelial cells (the cells that line breast ducts) and stromal cells (the connective tissue that supports the ducts). Fibroadenomas are not cancerous, and having a fibroadenoma does not increase the risk of developing breast cancer in the future.

If a fibroadenoma is removed completely, it does not grow back. However, new fibroadenomas can develop in either breast.

What are the symptoms of a fibroadenoma?

Fibroadenomas usually feel like round, firm, smooth lumps in the breast. They are often painless and can move slightly under the skin when touched. Their size can change with shifts in hormone levels, for example during the menstrual cycle, pregnancy, or menopause.

What causes a fibroadenoma?

The exact cause of fibroadenoma is not fully understood, but several factors are believed to play a role:

  • Hormones – Estrogen and other reproductive hormones stimulate fibroadenomas. They often grow during times of hormonal change, such as puberty, pregnancy, or hormone therapy.

  • Genetics – Fibroadenomas can run in families, suggesting a genetic component.

  • Local growth factors – Certain signals in breast tissue may promote the growth of stromal and glandular cells, leading to fibroadenomas.

  • Trauma or injury – Rarely, breast injury may trigger changes that resemble fibroadenoma.

  • Lifestyle and diet – While not a direct cause, diet and hormone-related factors may influence risk in some individuals.

How is the diagnosis made?

A fibroadenoma is diagnosed by a pathologist who examines a tissue sample under the microscope.

  • Biopsy – A small piece of tissue may be removed using a needle. Sometimes, the term fibroepithelial lesion is used in the biopsy report when the sample is too small to confirm fibroadenoma or another similar tumor.

  • Excision – The entire lump may be surgically removed and examined. A full excision allows the pathologist to make a definite diagnosis.

Microscopic features

Under the microscope, a fibroadenoma is made up of ducts surrounded by stroma (fibrous connective tissue). The ducts are lined by normal epithelial cells, while the surrounding stroma contains fibroblasts (supporting cells).

The amount of stroma can vary:

  • In younger women, the stroma is often more cellular (containing more fibroblasts).

  • In older women, the stroma may become less cellular and more fibrous, a process called sclerosis or hyalinization.

Growth patterns

Pathologists describe two common growth patterns in fibroadenomas:

  • Intracanalicular fibroadenoma – The ducts are compressed and distorted by the surrounding stroma.

  • Pericanalicular fibroadenoma – The ducts remain round and open, surrounded by stroma.

These growth patterns do not affect behavior or outcome.

Other changes in fibroadenoma

Fibroadenomas can show a variety of other noncancerous changes. These changes are common and do not increase the risk of cancer.

Examples include:

Margins

A margin is the normal tissue surrounding a tumor that is removed during surgery.

  • A negative margin means no tumor is seen at the cut edge.

  • A positive margin means tumor cells are present at the cut edge.

Because fibroadenoma is benign, reports often simply state that the lesion was completely excised or that margins are negative. Margins are only reported when the entire fibroadenoma has been removed.

Margin

Questions to ask your doctor

  • Was my diagnosis confirmed as fibroadenoma or described as a fibroepithelial lesion?

  • Do I need to have the fibroadenoma removed, or can it be monitored?

  • Were there any other changes (such as microcalcifications) in my fibroadenoma?

  • If removed, were the margins clear?

  • Am I at risk of developing new fibroadenomas in the future?

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