Fibroadenoma

by Livia Florianova, MD FRCPC
March 9, 2022

What is a fibroadenoma?

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

How do pathologists make the diagnosis of fibroadenoma?

The diagnosis of fibroadenoma 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?

When examined under the microscope, a fibroadenoma is made up of epithelial cells and fibroblasts. The epithelial cells in a fibroadenoma connect to form ducts that are surrounded by fibroblasts and stroma. Pathologists use the term ‘stromal cellularity’ to describe the number of fibroblasts in the stroma surrounding the ducts in the fibroadenoma. 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.

Are there different types of fibroadenomas in the breast?

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.

What other changes may be seen in a fibroadenoma?

There are many other non-cancerous changes that 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:

• Microcalcifications
• Sclerosing adenosis
• Usual ductal hyperplasia (UDH)
• Proliferative changes
• Columnar cell change
• Fibrocystic changes
• Apocrine metaplasia

​What is a margin?

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.