What is a fibroadenoma?

A fibroadenoma is a solid, not liquid-filled, lump found in the breast. They 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 breast cancer.

What does a fibroadenoma feel like?

If you have a fibroadenoma, it may feel like a marble under the surface of the skin. They 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.

It’s important to note that they may vary in size. Some are so small, they are only detected during imaging, such as during a mammogram or on an ultrasound. Others are quite large, spanning several inches across the breast. 

Different types

About 10 percent of women have a fibroadenoma at least once in her lifetime. Fibroadenomas typically show up in your 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. 

• Most fibroadenomas are simple fibroadenomas. When viewed under a microscope, they appear uniform in appearance. 
• Yet some fibroadenomas have more complex features. These complex fibroadenomas are usually found in older people and are often larger than simple fibroadenomas (1.9 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.

Possible causes

What causes fibroadenomas to form isn’t certain, but it’s possible that the female reproductive hormone estrogen plays a role. 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. 

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.

Diagnosis

Diagnosing a fibroadenoma starts with a review of your 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 your 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. 

An 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 piece of rice. You 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 the 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.

Treatment

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

Your doctor may recommend removing them or monitoring them, depending on the circumstances. 

Sometimes monitoring makes the most sense in these 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 your 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 you pain.
• The results of a needle biopsy were unclear. 
• There are concerns about breast cancer.

Removal may involve these options:

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 you, the patient, want 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. 

You’ll 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.