Author Lisa Wiechmann MD



Fibroadenomas are benign breast disorders that usually arise in the developed breast during the 15-25 year period (occasionally in older women). They are believed to be caused by estrogen induced hyperplasia of a single lobule and if they are allowed to grow, they can reach 2-3 cm in diameter. (exception: giant fibroadenoma, occur in puberty, more common in the Afro-Caribbean population, often rapidly growing, resected by enucleation)

1: 200 fibroadenomas shows infarction, and this is more common in pregnancy and lactation.

Occasionally the term fibroadenoma may be used to describe any benign , confined tumor of the breast that has both mesenchymal and glandular elements. Therefore the term may encompass a number of specific variants including hamartomas, tubular adenomas, lactating adenomas, adenolipoma, juvenile fibroadenoma (occur around menarche) and giant adenoma (> 5 cm).

Fibroadenomas often clinically present as a rubbery mass that is movable and unfixed to surrounding breast tissue

Traditionally, the risk for subsequent carcinoma in patients with typical fibroadenoma has not been considered higher than for the general population. Recent data has shown that a small percentage of fibroadenomas have given rise to carcinomas. In this setting lobular carcinoma in situ is the predominant type.


Microscopically a fibroadenoma is mostly composed of fibrous tissue. Stromal and parenchymal arrangement define the microscopic architecture as intracanalicular (epithelium is stretched out into curvilinear arrangement), pericanalicular (stroma surrounds duct like epithelial structures) or mixed.

This classification is of no practical or prognostic importance.


Fibroadenomas represent the 3rd most common type of breast lesion after fibrocystic disease and carcinoma. They are usually solitary, but they may present as multiple lesions in 10%-15% of cases. Although they have a typical clinical appearance, the diagnosis of fibroadenoma is accurate in only 50% of cases. However, in women less than 20 years of age it accounts for approximately 75% of breast biopsies.

Fibroadenomas represent the most common benign solid tumor in women of child-bearing age  and overall
7% of breast “lumps” are fibroadenomas

Population Group

The Afro-Caribbean population has a higher incidence of the disease when compared to whites

Sex Distribution

female disease

Age Distribution

Fibroadenomas commonly present in young females ages 15-25 yrs, though the range of presentation includes ages 13-80 yrs. Fibroadenomas represent the most common benign breast tumors in women under the age of 35 yrs.

Dietary Factors

No dietary factors have been correlated with the formation of fibroadenomas

Predisposing Factors

Because estrogen is thought to play a, pregnancy and lactation. Estrogen replacement therapy and contraceptive medications may also have a role.

Etiologic Agent



Fibroadenomas are thought to be the result of an aberration in the process of lobular development. Hormonal factors appear to play a significant role in their formation. As we know from physiology changes in breast size and shape begin at puberty and are due to growth or involution of both glandular and stromal elements of the breast. Three types of lobules have been described: Type 1(or virginal) consists of a cluster of 11 buds around a terminal duct; it is the predominant type found in nulliparous and postmenopausal women and cells in this type of lobule proliferate at the highest rate. Type 2 lobules contain an average of 47 buds, and type 3 lobules have 80 and predominate in parous women. The presence of estrogen receptor-alpha and the progesterone receptor in these lobules is proportional to the rate of proliferation. As fibroadenoma is the result of an aberration of lobular development, it is evident after this brief overview, how estrogen stimulation in pregnancy, adolescence and exogenous unopposed estrogen replacement therapy determines its growth.


Because the breast epithelium is responsive to hormones it may undergo changes during adolescence and pregnancy including infarction, inflammation and degeneration (approximately 1:200 fibroadenomas show infarction). Dystrophic calcification may occur and mimic carcinoma. Although historically it has been widely accepted that fibroadenomas do not confer an increased risk of breast cancer, recently four population based retrospective studies have shown a small (relative risk 1.3-1.9) but significant risk for breast cancer development that persists over time. More than 160 cases of associated cancers have been reported in the literature.

Natural History

Fibroadenomas are the result of aberrant lobular formation and typically grow to the size of approximately 2-3 cm. Occasionally they can grow to exceed 5 cm in diameter (giant fibroadenoma). Fibroadenomas undergo involution during menopause.

Gross Pathology

The gross appearance of fibroadenomas is usually characteristic and often diagnostic. They have a sarp circumscription and smooth boundaries and the cut surface is white and shiny with light brown areas if there is a significant epithelial component. Occasionally there can be calcifications, more commonly in older women. Most fibroadenomas measure 2-3 cm in diameter ranging 1- 15 cm. They can be solitary or multiple (15%). They are bilateral in 4% of cases. The most common location is the upper outer quadrant of the breast


13545 breast + dx juvenile fibroadenoma + histopathology hp Courtesy Frank Reale MD DB

Histologically, smooth muscle is a very rare component of fibroadenomas, fat is rare as is squamous metaplasia. Apocrine metaplasia may occasionally be present. Epithelial components show proliferation of epithelial ductal structures with branching and budding and fibrous stroma varies from myxoid and hypocellular to fibrous and hypercellular.  Special variants of fibroadenomas have been recognized as special entities: hamartoma, lactating adenoma, adenolipoma, juvenile fibroadenoma and giant fibroadenoma represent such entities.

13546 breast + dx juvenile fibroadenoma + histopathology hp Courtesy Frank Reale MD

Hamartomas are lesions made up of recognizable lobular units; they contain fat and have sharp, smooth borders, features which allow their recognition radiographically. Their average age of presentations is approximately two decades after fibroadenomas and the lesions are thought to be developmental rather than neoplastic. A similar lesion is the adenolipoma.

Other variants of fibroadenoma appearing in the younger age range are characterized by hypercellularity of stromal/ parenchymal structures. They bear some resemblance to benign Phylloides tumors of some other classification. Juvenile fibroadenomas tend to occur in adolescents and are notable for rapid growth and large size.. They occur around the time of menarche and frequently have a ductal pattern of epithelial hyperplasia as well as stromal hypercellularity. They do not have a tendency to local recurrence.


13543 breast + dx fibroadenoma histopathology cytopathology Courtesy Frank Reale MD DB

Fibroadenomas have both a stromal and parenchymal component. The cells can exhibit pleomorphism and metaplasia (apocrine more often than squamous)

Clinical Presentation

Fibroadenomas clinically present as firm, rubbery, (sometimes lobulated) mobile breast masses that are palpable and appear to be discrete from the remainder of the breast tissue. Fibroadenomas may increase in size during pregnancy and during unopposed estrogen replacement therapy, and may infarct following childbirth and lactation, becoming painful. Size may also vary with menstrual cycle. They can be solitary or multiple (10-15% cases multiple, 4% bilateral).

About 55% of fibroadenomas present in the left breast and are more commonly located in the upper outer quadrant


Because fibroadenomas appear in the younger female population, mammography is not the ideal diagnostic imaging modality, due to the density of the breasts and to the difficulty of interpretation of such images.

42913 Courtesy Priscilla Slanetz MD breast Case 8 hx 41 year old for screening fx mass dx fibroadenoma mammogram mammography typically younger patients, usually < 30 years multiple in 7-16% Imaging hypoechoic ovoid well circumscribed

42914 Courtesy Priscilla Slanetz MD breast Case 8 hx 41 year old for screening fx mass dx fibroadenoma mammogram mammography typically younger patients, usually < 30 years multiple in 7-16% Imaging hypoechoic ovoid well circumscribed

42726 Courtesy Priscilla Slanetz MD code breast fx mass dx fibroadenoma mammogram mammography

Sonographic evaluation, on the contrary, is of great utility in this patient population. Fibroadenomas appear as round or oval mass with homogenous, low level internal echoes. ( 30% fibroadenomas lack these “classical” features).

14594 breast fx mass fx solid dx fibroadenoma USscan Courtesy Carl D’Orsi MD

Occasionally fibroadenomas in older patients may demonstrate “popcorn” calcifications.

11166 Courtesy Carl D’Orsi MD BI RADS Mammographic Feature Analysis code breast fx coarse popcorn calcification dx benign dx probably involuting fibroadenoma mammogram mammography

11167 Courtesy Carl D’Orsi MD BI RADS Mammographic Feature Analysis code breast fx coarse popcorn calcification dx benign dx probably involuting fibroadenoma mammogram mammography

Surgical Management

Management of fibroadenomas is controversial. Historically it was felt that the presence of fibroadenomas did not correlate with an increased risk of decveloping breast cancer, but the literature has recently reviewed over 160 cases of breast carcinoma arising in the setting of fibroadenomas. There is no current recommendation for managing fibroadenomas. Expectant management is acceptable in the young female population where the risk of malignant disease is minimal. In this setting observation through several menstrual cycles is advocated by some. Overall, diagnosis can be confirmed by FNA (fine needle aspiration). Excisional biopsy is advised in the population over 25 and when the size of the fibroadenoma increases.