Fibroadenoma

Hamartoma

Age

Any age, most frequent in women younger than 30 y old, frequently peri- and postpubertal adolescents

Any age, usually women in 4th or 5th decade

Presentation

Slow-growing, usually solitary, firm, mobile mass, typically less than 3 cm but may be larger

Soft palpable mass or asymptomatic, detected on imaging

Location

Anywhere in the breast or along the milk line

Anywhere in the breast

Imaging findings

Well-circumscribed, ovoid or multilobulated mass on mammogram; hypoechoic mass on ultrasound, wider than tall with distinct margins

Mammographically a well-circumscribed, round to oval mass containing fat and soft tissue with a thin, radiopaque pseudocapsule; by ultrasound, a circumscribed, round to oval mass, which may have intralesional heterogeneous echogenicity

Histology

1. Circumscribed, ovoid mass, smooth interface with surrounding mammary tissue, nonencapsulated (Fig. 7.1.1)

2. Ratio of stromal and glandular proliferation remains consistent throughout the lesion (Fig. 7.1.2)

3. Intracanalicular (glands compressed into cords by proliferating stroma) (Fig. 7.1.3) and pericanalicular (stroma surrounds epithelial elements with open lumina) patterns, admixed in most lesions; no clinical significance to patterns

3. Stroma uniform in cellularity and distribution, composed of mixture of collagen and bland, non-atypical stromal cells with ovoid nuclei (Fig. 7.1.3)

4. Rare stromal mitoses (less than 3 in 10 high-powered fields [HPF])

5. The stroma may show a spectrum of changes, including multinucleated giant cells, myxoid change, PASH, hyalinization ± calcification, and rarely ossification

6. The epithelial component may show usual hyperplasia which is frequently mitotically active in adolescents, resembling gynecomastia

1. 
   

   Lobulated mass incorporating normal mammary ducts, lobules and interlobular fibrous tissue within adipose tissue in varying proportions (Fig. 7.1.4)

   
   
2. 
   

   Ducts and lobular units have a normal architectural arrangement (Figs. 7.1.4 and 7.1.5)

   
   
3. 
   

   Demarcated from surrounding breast tissue by a thin, delicate capsule (Fig. 7.1.4)

   
   
4. 
   

   Epithelial elements may show fibrocystic changes

   
   
5. 
   

   Stroma may contain pseudoangiomatous stromal hyperplasia (PASH) or smooth muscle (myoid hamartoma)

   
   
6. 
   

   Not easily diagnosed on core needle biopsy as complete architecture lacking

Special studies

None to distinguish from mammary hamartoma

Should be interpreted in radiologic context, which is usually defining

Genetic abnormalities

Numerical abnormalities of chromosomes 16, 18, and 21; MED12 and RARA mutations

May be seen in association with Cowden’s syndrome. Aberrations involving 12q12-15 and 6p21 have been described.

Treatment

None required; may be excised for cosmesis if large or disfiguring

None necessary. Well-defined border/capsule usually allows for enucleation.

Clinical implication

Development of additional fibroadenomas

None. Rare local recurrences are of no consequence.

Fibroadenoma

Cellular Fibroadenoma

Age

Any age, most frequent in women younger than 30 y old; frequently peri- and postpubertal adolescents

Women younger than 30 y

Presentation

Slow-growing, solitary, mobile mass, typically less than 3 cm but may be larger; occasionally multiple and/or bilateral

Solitary, firm, palpable, mobile mass, typically less than 3 cm but may be larger; occasionally multiple and/or bilateral; may have history of rapid growth, otherwise no clinical findings to distinguish from ordinary fibroadenoma

Location

Anywhere in the breast or along the milk line

Anywhere in the breast or along the milk line

Imaging findings

Well-circumscribed, ovoid or multilobulated mass on mammogram; hypoechoic mass on ultrasound, wider than tall with distinct margins

Well-circumscribed, ovoid or multilobulated mass on mammogram; hypoechoic mass on ultrasound, wider than tall with distinct margins; no imaging findings to distinguish fibroadenoma from cellular fibroadenoma

Histology

1. 
   

   Circumscribed, ovoid mass; smooth interface with surrounding mammary parenchyma; nonencapsulated (Fig. 7.2.1)

   
   
2. 
   

   Proliferation of stromal and epithelial elements; ratio of stroma and glands remains relatively consistent throughout the lesion

   
   
3. 
   

   Two patterns, intracanalicular (glands compressed into cords by proliferating stroma) and pericanalicular (stroma surrounds epithelial elements with open lumina), are admixed in most lesions; no clinical significance to patterns. Intracanalicular pattern may mimic benign phyllodes tumor (Fig. 7.2.2)

   
   
4. 
   

   Stroma is uniform in cellularity and distribution, composed of a mixture of collagen and bland, non-atypical stromal cells with ovoid nuclei (Fig. 7.2.3)

   
   
5. 
   

   Little mitotic activity (<3/HPF)

1. 
   

   Circumscribed, ovoid mass, smooth interface with surrounding mammary tissue, nonencapsulated (Fig. 7.2.4)

   
   
2. 
   

   Proliferation of stroma and epithelial elements; ratio of stroma and glands usually remains consistent throughout the lesion (Fig. 7.2.4); both intracanalicular and pericanalicular patterns common

   
   
3. 
   

   Increased stromal cellularity, but limited mitotic activity (usually <3/10 HPF) (Figs. 7.2.5 and 7.2.6)

   
   
4. 
   

   Stromal cells lack atypia (Fig. 7.2.6)

Special studies

None to distinguish from cellular fibroadenoma

None to distinguish from ordinary fibroadenoma

Genetic abnormalities

Numerical abnormalities of chromosomes 16, 18, and 21; MED12 and RARA mutations

Numerical abnormalities of chromosomes 16, 18, and 21; MED12 and RARA mutations

Treatment

None required; may be excised for cosmesis if large or disfiguring

None required; may be excised for cosmesis if large or disfiguring

Clinical implication

Development of additional fibroadenomas

The descriptors “giant” or “juvenile” fibroadenoma are clinical terms that describe rapid growth. The histologic correlate of these clinical terms is a cellular fibroadenoma that may show abundant hyperplasia that resembles gynectomastia. Mitotic activity in the epithelium and stroma (focally up to 5/10 HPF) is a result of hormonal stimulation and not an indication of aggressive clinical behavior.

Cellular Fibroadenoma

Benign Phyllodes Tumor

Age

Women younger than 30 y

Generally a decade older than women with fibroadenomas, occasionally younger women

Presentation

Solitary, firm, palpable, mobile mass, typically less than 3 cm but may be larger; occasionally multiple and/or bilateral; no clinical findings to distinguish from benign phyllodes tumor

Solitary, firm, palpable, mobile mass, frequently larger than 5 cm; very rarely multiple and/or bilateral; no clinical findings to distinguish from cellular fibroadenoma

Imaging findings

Well-circumscribed, ovoid or multilobulated mass on mammogram; hypoechoic mass on ultrasound, wider than tall with distinct margins; no imaging findings to consistently distinguish fibroadenoma from benign phyllodes tumor

Round, oval or lobulated, well-circumscribed mass on mammogram, may have a radiolucent halo; on ultrasound, inhomogeneous, solid mass containing cleft-like cystic spaces with posterior acoustic enhancement

Histology

1. 
   

   Circumscribed, ovoid mass, smooth interface with surrounding mammary parenchyma, nonencapsulated (Fig. 7.3.1)

   
   
2. 
   

   Proliferation of stroma and epithelial elements; ratio of stroma and glands usually remains consistent throughout the lesion (Fig. 7.3.2); both intracanalicular and pericanalicular patterns common

   
   
3. 
   

   Increased stromal cellularity, but limited mitotic activity (usually <3/10 HPF) (Figs. 7.3.3, 7.3.4, 7.3.5)

   
   
4. 
   

   Stromal cells lack atypia (Fig. 7.3.5)

1. 
   

   Circumscribed, lobulated proliferations of epithelium and expanded stroma, classically with a leaf-like architecture (Figs. 7.3.6 and 7.3.7)

   
   
2. 
   

   The epithelium-bound leaf-like structures project into prominent epithelial-lined clefts formed by the expanded stroma (Figs. 7.3.7 and 7.3.8). Epithelial distribution fairly regular throughout the lesion.

   
   
3. 
   

   Stroma characterized by bland, spindled cells with mild atypia and mildly increased mitotic activity (usually <5/10 HPF) (Figs. 7.3.9 and 7.3.10); stroma may be condensed around epithelial clefts. Stromal expansion may be uniform or heterogeneous. Stromal overgrowth absent

   
   
4. 
   

   Squamous metaplasia common (rare in fibroadenoma)

   
   
5. 
   

   Distinction between benign phyllodes tumor and cellular fibroadenoma may be difficult with the limited sample provided by core needle biopsy

Special studies

None to distinguish from benign phyllodes tumor

None to distinguish from fibroadenoma

Genetic abnormalities

Numerical abnormalities of chromosomes 16, 18, and 21; MED12 and RARA mutations

Heterogeneous cytogenetic abnormalities. Mutations of MED12 and RARA, FLNA, SETD2, and KMT2D reported.

Treatment

None required; may be excised for cosmesis if large or disfiguring

Excision; circumscription of benign phyllodes tumor may result in positive margin due “shelling-out.” Clinical follow-up preferable to reexcision to maintain cosmesis.

Clinical implication

May develop additional fibroadenomas

Recurrence rates slightly higher than cellular fibroadenoma, approximately 10-15%