Fibroadenomas

ALSO KNOWN AS: Complex fibroadenomas, juvenile fibroadenomas, giant fibroadenomas

RELATED CONDITIONS: Fibrocystic breast disease, phyllodes tumors, breast cysts

DEFINITION: Fibroadenomas are benign breast tumors that are characteristically smooth-surfaced, round or oval in shape, and freely movable on palpation (feeling with the fingers). They can range in size from 1 to 15 centimeters (cm). A fibroadenoma consists of homogeneous (closely related) fibrous tissue. In rare instances, a fibroadenoma can contain a breast cancer. This is more likely in a complex fibroadenoma.

A complex fibroadenoma contains several specific tissue changes. They are sclerosing adenosis (hardening of glandular breast tissue) and apocrine metaplasia (conversion of milk-producing cells into an abnormal form). Although a fibroadenoma is not considered a precursor to breast cancer, it is thought that having a complex fibroadenoma slightly increases a woman’s risk of developing breast cancer in the future.

Juvenile and giant fibroadenomas occur only in teenagers or young adults and can grow as large as 15 cm, although 10 cm is usually the upper limit. Malignant phyllodes tumors (also called periductal stromal tumors) are a rare type of breast cancer that can occur within a fibroadenoma. Typically, this type of cancer does not spread beyond the breast tissue.

Risk factors: Fibroadenomas require the presence of estrogen to develop and grow, so they occur between menarche, the onset of menstruation, and menopause. Generally, after menopause, an existing fibroadenoma will stop growing and may even disappear. If a woman takes estrogen after menopause, she can develop a fibroadenoma.

Etiology and the disease process: A fibroadenoma arises from a single milk duct in the breast and is made up of both glandular (milk-producing cells) and epithelial cells (skin cells that line the duct). There is no fluid inside a fibroadenoma. It develops from an overgrowth of the affected breast tissue. The cause of the overgrowth of tissue remained a mystery to medical researchers in the mid-2020s, although estrogen is required for fibroadenoma development, so causes are believed to be hormonal.

Fibroadenomas generally stop growing at 2 to 3 cm, although they occasionally grow larger. They may also enlarge during pregnancy and at times of higher estrogen levels during the menstrual cycle.

Immunosuppressive medications appear to affect the growth and development of fibroadenomas. Studies have demonstrated that 50 percent of women who receive the immunosuppressive drug cyclosporine after a kidney transplant will develop one or more fibroadenomas.

Incidence: Fibroadenoma is the most common type of benign breast tumor, although the reported incidence of fibroadenoma varies with publication. Twenty-five percent of women will develop a fibroadenoma at some time during their lives. Roughly one-third of fibroadenomas are complex fibroadenomas.

Symptoms: In women younger than age thirty-five, fibroadenomas usually appear as palpable (can be felt) breast masses. After age thirty-five, they may be discovered as a palpable breast mass, or they may appear on mammography as a breast mass that is not palpable. Fibroadenomas are not painful.

Screening and diagnosis: Screening is not carried out specifically for fibroadenomas, but some are picked up while screening for breast cancer in women over the age of forty. Breast fibroadenomas may be diagnosed by breast self-examination if they are palpable, or by mammography. On a mammogram, a fibroadenoma appears as a dense area in the breast, and in women over age forty, it may have areas of calcification (mineral deposits). Since it is not possible to determine whether a breast density is a fibroadenoma or breast cancer on mammography, subsequently, a breast ultrasound is performed. On an ultrasound, a fibroadenoma looks like a clear area with defined edges, much as a breast cyst does. The only way to determine whether a density is, indeed, a fibroadenoma is to biopsy it. A biopsy may be performed using a fine needle, a core needle, or a surgical incision. A pathologist examines the tissue under a microscope and decides whether it is cancer or a fibroadenoma. In ascertaining whether a fibroadenoma is malignant or benign, doctors began using a triple assessment approach which combines a breast exam, imaging, and percutaneous tissue study.

A cancer is present inside less than 1 percent of fibroadenomas. Typically, these fibroadenomas are larger than usual and have irregular margins that are less clearly defined. In 1 percent of cases, what appears to be a fibroadenoma is actually a malignant phyllodes tumor.

Because a fibroadenoma is not cancer, there is no staging for it. If breast cancer is found within a fibroadenoma, it is staged as a breast cancer.

Treatment and therapy: A fibroadenoma may be totally removed at the time of biopsy by surgical excision or core needle biopsy. If it is not removed, it will be monitored annually for growth and changes by mammography, (MRI), or ultrasound. Advances in the treatment of fibroadenoma include the use of cryoablation, a minimally invasive procedure that uses liquid nitrogen to destroy the fibroadenoma.

Prognosis, prevention, and outcomes: Since fibroadenomas are benign tumors, the prognosis is excellent for women who develop them. There is a slight increase in the risk of subsequently developing breast cancer. Before menopause, there is no way to prevent a fibroadenoma from developing. After menopause, a woman can prevent a fibroadenoma by avoiding any type of systemic estrogen therapy.

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