As the name implies it is composed of both fibrous and glandular tissue. It is benign. A firm, rubbery, painless mass in the breast of a woman under 25 will almost always be a fibroadenoma. If left alone it can continue to grow and ulcerate through the skin . It is by far the most common breast tumor in women under 25.
Some fibroadenomas are polyclonal hyperplasias.
Polyclonal fibroadenomas occur in almost half the women receiving cyclosporin for renal transplantation.