Fibroadenoma

Pathogenesis

• A benign biphasic tumour composed of fibrous stromal and epithelial (ductal) elements, hence also called adenofibroma.
• It occurs predominantly during reproductive life, especially at 15-30 years, supporting hormonal responsiveness.
• The proliferating fibrous stroma compresses and distorts the ducts. Both stromal and epithelial components are present, but the stromal component determines the architectural pattern.

Morphology

• Usually solitary, small, about 2-4 cm.
• A sharply circumscribed, apparently encapsulated, spherical or discoid mass.
• Cut surface: firm, grey-white, slightly myxoid, often with slit-like spaces produced by compressed ducts.
• A tumour up to 15 cm is termed a giant fibroadenoma. Multiple lesions occurring with fibrocystic disease are termed fibroadenomatosis.

• Shows proliferation of both ducts and fibrous stroma.
• Two characteristic patterns may coexist:

1. Pericanalicular pattern
   • Proliferating stroma surrounds the ducts.
   • Ducts retain a round or oval, open lumen.
2. Intracanalicular pattern
   • Proliferating stroma compresses and distorts ducts.
   • Ducts become elongated, slit-like, or cleft-like spaces.

Phyllodes tumour (formerly cystosarcoma phyllodes)

Pathogenesis

• An uncommon fibroepithelial breast tumour with a more pronounced stromal proliferation than fibroadenoma.
• Its older name, cystosarcoma phyllodes, is misleading: “cysto” and “sarcoma” do not necessarily indicate a cystic or malignant lesion. WHO prefers phyllodes tumour.
• The term phyllodes means leaf-like, referring to its gross and microscopic architecture.
• It is classified as benign, borderline, or malignant according to histological features.
• It occurs mainly in women aged 30-70 years and is usually much larger than a fibroadenoma.

Morphology

• Usually a large lesion, often 10-15 cm, round to oval and bosselated.
• Less completely encapsulated than fibroadenoma.
• Cut surface is grey-white and may show:
  • Cystic spaces/cavities
  • Slit-like clefts
  • Haemorrhage
  • Necrosis
  • Degenerative changes
• Characteristically has a leaf-like appearance, caused by stromal projections into cystically dilated spaces.

• Biphasic lesion with:
  1. Branching benign ducts, often showing epithelial hyperplasia and papillary projections.
  2. Markedly increased fibrous stroma, often with a myxoid appearance.
• The key distinction from fibroadenoma is greater stromal cellularity.
• Stromal tissue projects into cleft-like spaces lined by epithelium, producing the characteristic leaf-like pattern.

Histological grading of phyllodes tumour

• Mitotic activity
• Stromal cellularity
• Stromal cellular atypia
• Nature of tumour margins, especially infiltrative margins

Key difference