A fibroadenoma is a noncancerous (benign) type of breast tumor and the most common benign breast tumor, especially in women under the age of 35. It is made of two normal breast components growing together: epithelial cells (the cells that line the breast ducts) and the stroma (the connective tissue that supports the ducts). Because it contains both components, pathologists call it a fibroepithelial tumor. A fibroadenoma cannot spread to other parts of the body.
This article will help you understand the findings in your pathology report, what each term means, and why it matters for your care.
Fibroadenomas usually feel like round, firm, smooth lumps that can move slightly under the skin when touched. They are most often painless. Their size can change with shifts in hormone levels, for example during the menstrual cycle, pregnancy, or menopause. Some fibroadenomas are too small to feel and are found only on breast imaging such as ultrasound or mammography.
The exact cause of a fibroadenoma is not fully understood, but several factors are believed to play a role. Fibroadenomas are hormone-sensitive, meaning the hormone estrogen and other reproductive hormones stimulate their growth, which is why they often appear or grow during times of hormonal change such as puberty and pregnancy. Fibroadenomas can also run in families, suggesting a genetic component, and local growth signals within the breast tissue may encourage the stromal and glandular cells to grow together.
A fibroadenoma is diagnosed after breast tissue is examined under the microscope by a pathologist. The tissue is usually obtained by a core needle biopsy, and sometimes the whole lump is removed by surgery. Under the microscope, a fibroadenoma is made up of ducts surrounded by stroma. The ducts are lined by normal epithelial cells, and the stroma contains supporting cells called fibroblasts. In younger women, the stroma is often more cellular (containing more fibroblasts), while in older women it may become less cellular and more fibrous, a change called hyalinization. Pathologists may describe the growth pattern as intracanalicular (the ducts are compressed by the stroma) or pericanalicular (the ducts stay round and open); these patterns do not affect how the fibroadenoma behaves.
On a small core needle biopsy, a fibroadenoma with a cellular stroma can be difficult to tell apart from a phyllodes tumor, another fibroepithelial tumor that is treated differently. When the pathologist cannot be certain which one is present on a small sample, the report may use the general term fibroepithelial lesion. In that situation, the surgeon may remove the whole lump so the pathologist can examine all of it and make a definite diagnosis.
Not all fibroadenomas are the same. Your pathology report may describe one of the following:
Because a fibroadenoma is benign, many do not require any treatment and can simply be watched over time. The pathology findings, along with your imaging and preferences, guide which options your team discusses, rather than dictating a single path.
If a fibroadenoma is completely removed, it does not grow back, although new fibroadenomas can develop elsewhere in either breast.