A 28-year-old woman presents with a 6-month history of a gradually enlarging lump in the left breast. On examination, a 4 cm firm mass is palpated in the upper outer quadrant with skin dimpling and mild tenderness. Ultrasound reveals a heterogeneous mass with irregular margins, increased vascularity on Doppler, and a maximum dimension of 4.5 cm. Core needle biopsy shows benign stromal and epithelial components with increased cellularity. What is the most likely diagnosis?

Explanation

## Clinical Diagnosis: Phyllodes Tumour **Key Point:** Phyllodes tumours are benign or borderline fibroepithelial lesions that present with rapid growth, large size, and imaging features of increased cellularity and vascularity. Unlike fibroadenomas, they can undergo malignant transformation and require surgical excision. ### Differential Features: Fibroadenoma vs. Phyllodes Tumour | Feature | Fibroadenoma | Phyllodes Tumour | |---------|--------------|------------------| | Age of presentation | 15–35 years | 40–50 years (can be younger) | | Growth rate | Slow, stable | Rapid (weeks to months) | | Size | Usually < 3 cm | Often > 3 cm | | Skin changes | Absent | Dimpling, ulceration possible | | Margins on imaging | Sharp, well-circumscribed | Irregular, lobulated | | Vascularity | Minimal | Increased on Doppler | | Histology | Benign stromal and epithelial | Increased stromal cellularity | | Malignant potential | None | Yes (5–10% risk) | | Management | Observation | Wide local excision ± margins | **High-Yield:** **MNEMONIC: PHYLLODES = Proliferative, Heterogeneous, Younger (can present young), Large (> 3 cm), Lobulated margins, Overgrowth of stroma, Doppler vascularity, Excision required, Stromal cellularity.** ### Pathological Classification ```mermaid flowchart TD A[Phyllodes Tumour]:::outcome --> B{Stromal Cellularity & Mitotic Activity}:::decision B -->|Low| C[Benign]:::action B -->|Intermediate| D[Borderline]:::action B -->|High| E[Malignant]:::urgent C --> F[Wide local excision with margins]:::action D --> F E --> G[Wide local excision + consideration of chemotherapy]:::action ``` **Clinical Pearl:** Phyllodes tumours are named for their "leaf-like" histological appearance (Greek: phyllon = leaf). The stromal component overgrows relative to the epithelial component, distinguishing them from fibroadenomas where both are balanced. ### Why This Case Suggests Phyllodes Tumour 1. **Rapid growth** over 6 months (fibroadenomas grow slowly or remain stable). 2. **Large size** (4.5 cm — fibroadenomas are typically < 3 cm). 3. **Skin dimpling** — indicates aggressive local behaviour. 4. **Irregular margins and increased vascularity** on imaging — suggest stromal proliferation. 5. **Increased stromal cellularity on biopsy** — pathognomonic for phyllodes tumour. ### Management - **Wide local excision** with 1–2 cm margins is mandatory. - **Histopathological grading** (benign, borderline, malignant) determines adjuvant therapy. - **Malignant phyllodes** may require chemotherapy or radiotherapy. - **Recurrence rate** is 10–15% if margins are inadequate.