This page was reviewed under our medical and editorial policy by

Anita Johnson, MD, FACS, Chief of Surgery, Atlanta; Leader, Atlanta Women's Cancer Center

This page was reviewed on February 7, 2022.

A fibroadenoma is a noncancerous breast lump that's sometimes found by women during breast self-exams or by the care team during breast imaging. About 10 percent of women will have a fibroadenoma at least once in her lifetime.

What are fibroadenomas?

A fibroadenoma is a solid, not liquid-filled, lump found in the breast. Such lumps are among the many causes of breast changes and often shrink after menopause.

Breasts contain what are called stromal and epithelial connective tissue cells. These cells have receptors for the hormones, estrogen and progesterone. Fibroadenomas are formed from those two types of tissues.

In most cases, these lumps are simple, benign breast tumors that don’t lead to cancer or increase a woman’s risk for developing breast cancer.

Fibroadenomas are benign, and in rare cases they may become cancerous. One study found that the prevalence of fibroadenomas turning cancerous occurred in fewer than 1 percent of cases.

Fibroadenoma symptoms

Fibroadenomas may vary in size and may not cause symptoms. Some women may not know they have a fibroadenoma until a doctor detects one during imaging, such as during a mammogram or on a breast ultrasound. Others are quite large, spanning several inches across the breast. In some instances, the first symptom is a lump under the skin.

What does a fibroadenoma feel like?

A fibroadenoma may feel like a marble under the surface of the skin. These lumps usually are found in the upper, outer quadrant of the breast and have these features: 

  • They’re hard and round, with clearly defined edges.
  • They may move under the skin when touched.
  • They’re firm or rubbery.
  • They’re usually painless.

Types of fibroadenoma

The care team may take cells from a patient’s fibroadenoma and view them under a microscope to evaluate the type.

Simple fibroadenoma: Most fibroadenomas are simple fibroadenomas. When viewed under a microscope, they appear uniform in appearance. 

Complex fibroadenoma: When viewed under a microscope, some fibroadenomas have more complex features. These complex fibroadenomas are usually found in older people and are often larger than simple fibroadenomas (1.9 centimeter (cm) vs. 1.3 cm on average has been reported in studies of fibroadenomas). On an imaging scan, they may be seen with one or more features, such as an irregular shape, a variety of contours, microcalcifications and other changes.

Fibroadenoma causes

What causes fibroadenomas isn’t certain, but it’s possible that the female reproductive hormone estrogen plays a role in their formation. These lumps do seem to be influenced by hormones: They’re known to grow during pregnancy and shrink during menopause. They may also grow during puberty. Women who take oral contraceptives at a young age—before 20—have higher rates of fibroadenomas. Sensitivity to the hormones may cause an excessive proliferation of the connective tissues.

Fibroadenoma risk factors

A large cohort study of more than 58,000 women in JNCI Cancer Spectrum showed that several risk factors for fibroadenomas are similar to those for breast cancer, like education level and family history of breast cancer. Similar factors that appear to reduce the risk of breast cancer were also protective for fibroadenomas in the study, such as older age at first period, having more children and larger childhood body size. Further research is needed to validate these findings and identify which women are at highest risk of developing breast cancer after fibroadenoma, which is rare.

Fibroadenomas typically show up when a woman is in her 20s or 30s, but they may be found at any age. For women under 30, fibroadenomas are the most common benign breast tumor. They may also be found in children ages 10 to 18 years. When that happens, they are called juvenile fibroadenomas.

Fibroadenoma diagnosis and detection

Diagnosing a fibroadenoma starts with a review of the patient's medical history and an exam. Certain factors may help lead to a diagnosis, including: 

  • Age
  • Family history of breast cancer 
  • Location

The next steps may include:

  • Mammogram
  • Ultrasound
  • Biopsy

A mammogram or breast ultrasound may be used to help identify the mass. 

A mammogram is a type of X-ray in which images are taken while the patient's breast is pressed between plastic plates. It’s more often used in women over 35 and is read by a radiologist. It may be used for screening or diagnosis. The fibroadenoma appears on these X-rays with smooth, round edges. 

A breast ultrasound is used for women younger than 35. It shows fibroadenomas as round or oval masses. The ultrasound uses sound waves—hence the name—to show whether a mass is solid or filled with fluid. 

A core needle biopsy involves removing breast tissue in a way that’s minimally invasive. The samples are about the size of a kernel of rice. The patient may expect some bruising, but usually not scarring.

A pathologist then examines the tissue under a microscope in a lab. 

  • Simple fibroadenomas look the same all over.
  • Complex fibroadenomas tend to be larger and irregularly shaped, and their tissue is more varied.

It’s often necessary to perform a biopsy to identify a lump as a fibroadenoma or something else, especially in women in their 20s and older.

Fibroadenomas may be hard to differentiate on an ultrasound or mammogram from a connective tissue tumor known as a phyllodes tumor. Those tumors are rare overall, but they’re most often  experienced by women in their 40s. The two types of lumps may be better differentiated with a core needle biopsy.

Fibroadenoma treatment

Fibroadenomas often go away on their own. Those that have not been removed typically shrink after menopause.  

The care team may recommend removing them or monitoring them, depending on the circumstances. 

Sometimes monitoring makes the most sense in the following cases:

  • Those that may be monitored have been confirmed to be fibroadenomas and not breast cancer. The monitoring is to ensure they’re not growing.
  • One reason not to remove them is if doing so would also require removing enough nearby breast tissue that it would change the shape and texture of the breast. This may also make it more difficult to read future mammograms. When this option is chosen, regular breast exams and imaging are important to ensure that the fibroadenoma doesn’t begin to grow.

Still, many doctors do recommend removing a fibroadenoma, especially if:

  • It’s growing.
  • It’s causing pain.
  • The results of a needle biopsy were unclear. 
  • There are concerns about breast cancer.

Removal may involve the options listed below.

Surgery: This is often recommended if the fibroadenoma is growing rapidly or is greater than 2 cm in size. It may also be the right choice if the patient wants the fibroadenoma removed. It may be removed by a surgical procedure called a lumpectomy, then sent to a lab to be evaluated. 

Cryoablation: This treatment freezes the fibroadenoma using a cryoprobe, which destroys the cellular structure of the fibroadenoma. A core needle biopsy must be performed before cryoablation to confirm that it is, in fact, a fibroadenoma. 

Radiofrequency ablation: This process uses high-frequency energy to destroy the fibroadenoma using an ultrasound to focus the energy beam without destroying nearby tissues. 

The patient will likely go home the same day after one of these procedures.

It’s possible for one or more new fibroadenomas to appear after one is removed. This is not the return of the previous fibroadenoma—it’s a new one, and should be addressed by a doctor as soon as it's discovered.

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