Fibroadenoma

Definition

Fibroadenoma is the most common benign breast tumour in women under 30. It is a biphasic tumour composed of epithelial (acinar and ductal) and stromal (fibroblastic) elements. Two histological patterns exist: pericanalicular (fibrous stroma encircles rounded acini) and intracanalicular (fibrous stroma compresses ducts into elongated slit-like clefts).

General / Essential Features

• Biphasic tumour: epithelial + fibroblastic stromal components
• Small acini and duct-like structures resembling normal breast tissue
• Fibrous stroma arranged around and between acini
• Epithelial clefts (slit-like) formed by fibrous compression — intracanalicular pattern
• Benign epithelium: regular nuclei, no atypia, no mitoses
• Well-circumscribed; usually encapsulated

Sites

• Upper outer quadrant of the breast (most common quadrant for all breast lesions)
• Typically solitary; multiple in 10–15% (giant fibroadenoma in juveniles)
• No specific lobar distribution

Pathophysiology

Fibroadenomas arise from the terminal duct–lobular unit (TDLU). Oestrogenic stimulation during reproductive years drives growth; lesions often enlarge during pregnancy and regress post-menopause. MED12 mutations (as in uterine fibroids) have been identified. Giant juvenile fibroadenoma occurs in adolescents and can be rapidly growing.

Etiology

• Hormonal: oestrogen-sensitive — common in reproductive years
• MED12 somatic mutations
• Black women of Caribbean or African descent: higher incidence of multiple/giant fibroadenomas
• Cyclosporine use after renal transplant — associated with giant fibroadenoma

Clinical Features

• Smooth, mobile, well-defined, non-tender breast lump ('breast mouse')
• Usually 1–3 cm; may be multiple
• No skin changes, no nipple discharge
• Triple assessment: clinical + ultrasound + FNAC/core biopsy
• Malignant transformation extremely rare (<0.1%)

Diagnosis

• Ultrasound: well-defined, homogeneous, hypoechoic lesion with gentle lobulations
• FNAC / core biopsy: confirms benign biphasic histology
• Mammography: in women over 35 — calcified fibroadenoma ('popcorn' calcification)
• MRI: for multiple lesions or in high-risk patients

Treatment

• Conservative management for lesions <3 cm with confirmed benign histology
• Surgical excision: for >3 cm, growing, or patient anxiety
• Vacuum-assisted biopsy excision: ultrasound-guided, no scar
• Annual review: to monitor size and exclude interval change