by Livia Florianova, MD FRCPC
November 16, 2023

A fibroadenoma is a non-cancerous type of breast tumour and the most common breast tumour in women under 40 years old. The tumour will not occur again if removed completely, however, new fibroadenomas may develop in the same breast or the breast on the opposite side of the body.

What are the symptoms of a fibroadenoma?

Fibroadenomas are usually round tumours that feel firm to the touch. Their size may change depending on the body’s hormonal status (for example pregnancy or menopause).

How is this diagnosis made?

This diagnosis can be made after a small sample of tissue is removed in a procedure called a biopsy. Some reports may use the term ‘fibroepithelial lesion’ to describe the changes seen on the biopsy. This is a descriptive diagnosis that pathologists use when they have not seen enough of the tumour to make a full diagnosis. The diagnosis of fibroadenoma can also be made after the entire tumour is removed surgically and sent to a pathologist for examination.

What does a fibroadenoma look like under the microscope?

Under microscopic examination, a fibroadenoma is made up of two types of cells – epithelial cells and fibroblasts. The epithelial cells in the tumour connect to form spaces called ducts that are surrounded by fibroblasts and a type of connective tissue called stroma. Pathologists use the term ‘stromal cellularity’ to describe the number of fibroblasts in the stroma surrounding the ducts in the tumour. The cellularity can be variable and may be slightly increased in younger women. On the other end of the spectrum, the stroma of a fibroadenoma may decrease in cellularity over time, in which case it may be called sclerosed or hyalinized.

fibroadenoma breast

What is the difference between an intracanalicular and a pericanalicular fibroadenoma?

The cells in a fibroadenoma can show two patterns of growth that pathologists describe as intracanalicular and pericanalicular. In the intracanalicular type, the ducts are compressed by large amounts of stromal tissue. In the pericanalicular type, the ducts are wide open and surrounded by stroma. The pattern of growth does not change the behaviour of the tumour over time.

What other changes may be seen in a fibroadenoma?

Many other non-cancerous changes can take place inside a fibroadenoma. None of these changes are associated with an increased risk of developing cancer in the future.

Other non-cancerous changes that can be seen in a fibroadenoma include:

​What is a margin and why are margins important?

A margin is the normal tissue that surrounds a tumour and is removed with the tumour at the time of surgery. A margin is considered ‘positive’ when the tumour cells are seen at the cut edge of the tissue. Because fibroadenoma is a non-cancerous tumour, the report may simply state that the tumour was completely excised, or that margins are negative. Margins are only described in your report after the entire tumour has been removed.


About this article

This article was written by doctors to help you read and understand your pathology report. Contact us if you have any questions about this article or your pathology report. Read this article for a more general introduction to the parts of a typical pathology report.

Other helpful resources

Atlas of Pathology
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