Breast Fibroadenoma is the most common benign breast tumour of young adult women, characterised by biphasic growth of both glandular and stromal tissue and a hypoechoic mass with smooth, well-defined borders.
Description
Breast fibroadenoma is a benign mixed tumour of the breast, most common in young adult women. It is characterised by biphasic proliferation of both glandular and stromal components.
Pathogenesis
Fibroadenomas are hypothesised to occur as a result of an abnormal response to hormonal stimulation. The glandular and stromal components of the breast tissue proliferate, leading to the formation of a tumour.
Stages
- Proliferation of epithelial and stromal elements in multiple lobules
- Confluence of the hyperplastic lobules
- Formation of fibroadenomatoid nodules
- Nodules coalesce to form fibroadenoma
Subtypes
Fibroadenomas can be categorised into two subtypes, which are determined based on histological patterns:
- Pericanalicular fibroadenoma: Characterised by the stromal proliferation around the glandular tissue, resulting in a proliferation of ducts that are surrounded by fibrous stroma. This pattern can create an appearance similar to a Swiss cheese pattern microscopically. This is the most common subtype, occurring in approximately 60% of cases.
- Intracanalicular fibroadenoma: The proliferative stromal tissue compresses and distorts the ducts, forming elongated, slit-like spaces, or clefts. This pattern accounts for about 40% of cases. Despite the difference in the histologic pattern, there is no difference in clinical behaviour between pericanalicular and intracanalicular fibroadenomas.
Other less common subtypes include the juvenile fibroadenoma, which is a larger and rapidly growing fibroadenoma that occurs in teenagers, and the giant fibroadenoma, which grows larger than 10 cm and may replace much of the breast tissue.
Epidemiology, Risk Factors & Associations
- Most common benign breast tumour in women under 30 years of age. Incidence decreases after 40 years of age.
- Increased incidence with early menarche and nulliparity (unopposed estrogen)
- Increased risk with cyclosporine use (immunosuppressive agent used to treat organ rejection post-transplant)
- May have family history especially in patients with multiple fibroadenoma.
- No significant association with breast cancer
Clinical Features
- Usually presents as a painless, palpable mass. Up to 15% have multiple.
- Smooth, round, and mobile on examination
- Can increase in size with pregnancy and regress after menopause
Complications
- Extremely rare malignant transformation to phyllodes tumour
Pathological Features
Histopathology
- Macroscopic: Well-circumscribed, rubbery, mobile mass
- Microscopic: Biphasic proliferation of glandular and stromal tissue
Radiological Features
General Features
- Lobulated mass with smooth, well-defined borders
- Growth pushes surrounding tissues without invasion
- Degenerating fibroadenomas may demonstrate progressive coarse calcification in a ring-like distribution, eventually forming a popcorn-like appearance.
- Nonenhancing internal septations within a mass are due to hypovascular fibrous bands
- A known fibroadenoma that continues to enlarge is concerning for phyllodes tumour.
MG
- Fibroadenomas typically present as well-circumscribed, round or ovoid masses on mammography. They may be solitary or multiple.
- The density of the lesion is usually equal to or slightly less than that of the surrounding breast parenchyma.
- Calcifications are infrequently seen within fibroadenomas but, when present, are typically coarse and popcorn-like. They are seen in around 10-15% of cases.
- Occasionally, fibroadenomas may demonstrate indistinct or spiculated margins, especially if they are rapidly growing or have associated cystic changes, which can mimic the appearance of malignancy.
US
- B-mode: Hypoechoic, well-circumscribed, round or oval mass with posterior acoustic enhancement. Thin, echogenic pseudocapsule may be seen.
- Colour: No colour flow or twinkle artefact
MRI
- T1: Isointense to breast tissue
- T2: Slightly hyperintense to breast tissue
- T1 Gad+: Lobulated mass which enhances slowly with persistent enhancement in delayed phases. Non-enhancing internal septations may be seen.
Grading and Staging
No grading or staging system
Diagnosis
Diagnosis is primarily made by clinical examination, ultrasound, and histologic confirmation after biopsy or excision.
Differential Diagnosis
- Phyllodes tumour: Typically, a rapidly enlarging mass in women over 40. On imaging, larger size (>2 cm), lobulated or indistinct margins, and heterogeneous enhancement with areas of low signal intensity on T2-weighted images may suggest phyllodes tumour. Histology is key to differentiation as it demonstrates leaf-like projections.
- Lactating Adenoma: Looks like a fibroadenoma, possibly also containing internal echogenic foci representing milk. It occurs in pregnancy usually arises in the third trimester. It may infarct and cause pain. It may regress following cessation of breast feeding.
- Invasive ductal carcinoma: Often found in older patients. It tends to present as a spiculated, irregular mass with heterogeneous enhancement on mammography. Axillary lymphadenopathy may be present.
- Breast cyst: Characteristically seen in premenopausal women. On ultrasound, anechoic round or oval masses with posterior acoustic enhancement are seen. Simple cysts can be distinguished from fibroadenomas by aspiration.
- Breast abscess: Commonly associated with lactation or mastitis. Clinically presents with pain, redness and warmth over the breast tissue. On imaging, complex fluid collection with surrounding inflammatory changes is typically observed.
- Intraductal papilloma: These are typically small, benign tumours that grow within the breast ducts. They classically present with bloody nipple discharge. Imaging features can overlap with fibroadenomas; however, the presence of dilated ducts or ductal discharge can suggest this diagnosis.
Management
Fibroadenomas do not require treatment unless they are symptomatic or enlarge over time. In such cases, surgical excision is the treatment of choice.