Phyllodes tumor

Rare (<1% of breast tumors). Peak age 40-50 (older than fibroadenoma).

WHO Classification & Prognosis

1. Benign (60-75%): <5 mitoses/10 HPF. Resembles FA. Low recurrence if cleared.
2. Borderline: 5-9 mitoses/10 HPF. Moderate stromal cellularity.
3. Malignant: $\ge$ 10 mitoses/10 HPF. Stromal overgrowth. Metastasis is hematogenous (Lung/Bone), not lymphatic (axillary dissection rarely needed).

Imaging findings

• General: Indistinguishable from FA on size alone, but often larger at presentation.
• US:
  • Well-circumscribed, lobulated.
  • Clefts/Cystic spaces: Fluid-filled slits within the solid mass (highly suggestive of Phyllodes).
  • Hypervascularity (nonspecific).
• MRI: T2 hyperintense cystic spaces.

Management (Crucial Exam Point)

• Diagnosis: Core biopsy often insufficient (heterogeneous); requires wide excision for full grading.
• Treatment: Surgical excision with wide margins ($\ge$ 1 cm recommended by many guidelines, though NCCN accepts "clear margins" for benign).
• Contrast with fibroadenoma: Fibroadenoma can be "shelled out" (enucleation); Phyllodes requires margins to prevent recurrence (20% recurrence rate).