Most fibroadenomas are about 1–3cm in size and are called simple fibroadenomas. When looked at under a microscope, simple fibroadenomas will look the same all over.
Simple fibroadenomas do not increase the risk of developing breast cancer in the future.
Some fibroadenomas are called complex fibroadenomas. When these are looked at under a microscope, some of the cells have different features.
Having a complex fibroadenoma can very slightly increase the risk of developing breast cancer in the future.
Occasionally, a fibroadenoma can grow to more than 5cm and may be called a giant fibroadenoma. Those found in teenage girls may be called juvenile fibroadenomas.