Fibroadenomas are benign (non-cancer) tumors made up of both glandular breast tissue and stromal (connective) tissue. They are most common in young women in their 20s and 30s, but they may be found in women of any age. The use of birth control pills before age 20 is linked to the risk of fibroadenomas.

Some fibroadenomas are too small to be felt and can be seen only when the breast tissue is removed and examined under a microscope, but some are several inches across. They tend to be round and have borders that are distinct from the surrounding breast tissue. They often feel like a marble within the breast. You can move them under the skin and they are usually firm and not tender. A woman can have one or many fibroadenomas.


Some fibroadenomas can be felt, but some are only found on an imaging test (like a mammogram). A biopsy(removing tissue to be checked under a microscope) is needed to know if a tumor is a fibroadenoma. Most fibroadenomas look the same all over when seen under a microscope and are called simple fibroadenomas. But some fibroadenomas contain other components (such as macrocysts, sclerosing adenosis, or mineral deposits). These are called complex fibroadenomas. 


Many doctors recommend removing fibroadenomas, especially if they keep growing or if they change the shape of the breast. Sometimes (especially in middle-aged or elderly women) these tumors stop growing or even shrink on their own, without any treatment. In this case, as long as the doctors are certain the masses are really fibroadenomas and not breast cancer, they may be left in place and watched to be sure they don’t grow. This approach is useful for women with many fibroadenomas that are not growing. In such cases, removing them all might mean removing a lot of nearby normal breast tissue, causing scarring that would change the shape and texture of the breast. This could also make future physical exams and mammograms harder to interpret.

It’s important for women who have fibroadenomas have breast exams regularly to make sure they are not growing.

Sometimes one or more new fibroadenomas grow after one is removed. This means that another fibroadenoma has formed – it does not mean that the old one has come back.

Link to cancer risk

Women with fibroadenomas have an increased risk of breast cancer – about 1½ to 2 times the risk of women with no breast changes.