A Guide to Breast Fibroadenomas

Learn About These Benign Breast Tumors and What They Mean

Fibrocystic Breast Tissue
Fibrocystic Breast Tissue on a Mammogram. Credit: National Cancer Institute

Fibroadenomas are one of the findings that can be seen on your mammogram. They are benign (not cancerous) breast tumors that are made of glandular and fibrous breast tissue. These lumps can occur alone, in groups or as a complex. If you have multiple or complex fibroadenomas, this may raise your risk of breast cancer slightly.


While doing your regular breast self-exam, you may feel a breast fibroadenoma. These feel firm, round, smooth, rubbery, and are movable. They are so mobile that women sometimes refer to them as “breast mice” because they tend to run away from your fingers. These masses may feel tender, especially right before your period, when it may swell due to hormonal changes.


Fibroadenomas range in size from one to five centimeters, (0.39 inches to nearly two inches). Giant fibroadenomas can be the size of a small lemon, about 15 cm (5.9 inches).

Appearance on Mammogram

Fibroadenomas appear as round or oval smooth-edged masses on a mammogram. The outline of the mass will be clearly defined, not blurry, or invading the adjacent spaces. Sometimes they are accompanied by coarse calcifications. Fibroadenomas can look like cysts or a well-contained tumor.


Your doctor or radiologist may send you to have an ultrasound study done. This occurs when the breast tissue is dense and it makes the lump difficult to visualize on a mammogram study. The fibroadenoma will be easier to distinguish from other tissue, because of the way it responds to sound waves. It will appear as a dark area, with a definite outline, homogeneous, round or oval, and may have smooth-edged bumps. If the ultrasound doesn’t give a definite result, the next study may be an MRI (magnetic resonance image). The most conclusive test is a fine needle biopsy or a core needle biopsy, to get a sample of the cells for a pathologist to examine.


Since fibroadenomas are benign, treatment will vary depending on your diagnosis. If it is small, painless, remains the same size, and a biopsy confirms a benign (non-cancerous) finding, you would not need further treatment, but may have follow-up ultrasounds. However, if it is large (more than three cm), painful, growing, or a biopsy reveals atypical (very active) cells, you can have it surgically removed with a lumpectomy. If you qualify, you can have fibroadenomas removed with a laser ablation (using heat) or cryoablation (freezing). In-situ ablation of fibroadenomas can be done in-office, leaves tiny scars, and has a fast recovery.


The exact cause of fibroadenomas is unknown. They seem to be influenced by estrogen because they appear most often in premenopausal or pregnant women, or in women who are postmenopausal and taking HRT (hormone replacement therapy). Most fibroadenomas change in size during your menstrual cycle, when your hormone levels are changing. Thus, during the menstrual cycle, the same adenoma can become more noticeable or it may shrink to the point where it is not readily palpable.

When Do Fibroadenomas Develop?

These are most common in women who are from 15 to 30 years old and in pregnant women. Fibroadenomas occur in 10 percent of all women but in 20 percent of African-American women. They are much less common in postmenopausal women unless the women are on estrogen therapy. About 10 percent of all fibroadenomas will disappear over time, and twenty percent of them will recur. If they don’t disappear, they usually stop growing when they reach two or three centimeters.

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Article Sources
  • Fibroadenomas, American Cancer Society, Updated 06/10/2015.
  • NSW Breast Cancer Institute. Fibroadenoma of the breast. Last Updated: January 2014. Fibroadenoma of the breast (PDF document).