Phyllodes tumour

Phyllodes tumour is a tumour of the intralobular breast stroma. It may be benign or malignant.

Phyllodes tumour
Diagnosis in short
Phyllodes tumour. H&E stain.
LM	either (1) or (2): (1) large slit-like spaces, (2) cellular stroma - may be myxoid; +/-infiltrative border, +/-mitoses, +/-nuclear atypia, +/-"stromal overgrowth" ~ stroma fills microscopic field
Subtypes	benign, borderline, malignant
LM DDx	fibroadenoma, metaplastic breast carcinoma, primary breast sarcoma, other sarcomas
Gross	mass with clefts - leaf-like structures
Site	breast
Signs	mass lesion
Prevalence	uncommon
Prognosis	usually benign, may be malignant
Clin. DDx	other breast tumours - often fibroadenoma
Treatment	wide excision

It was previously called cystosarcoma phyllodes.

General

• The name comes from the word "leaf".
  • With imagination or psychotropic drugs, it may look like one: the epithelial component = the veins of the leaf.
• Wide excision -- this differs from fibroadenoma (just local excision).
• Approximately 6% are malignant.

Notes:

• There are case reports of phyllodes tumours in the prostate gland.
• Outside of the breast a phyllodes-like histomorphology may represent an adenosarcoma.

Gross

• Clefts/leaf-like structures.
• Friable - especially vis-à-vis a fibroadenoma.

Image:

• Benign phyllodes tumour (rsna.org).

Microscopic

Features - either 1, 2 or both of the following:

1. Large slit-like spaces - key feature. †
2. Cellular stroma - key feature. †
   • May be myxoid.

• +/-Infiltrative border.
• +/-Mitoses.
• +/-Nuclear atypia.
• +/-"Stromal overgrowth" ~ stroma fills microscopic field (see below).

Notes:

• † Large slit-like spaces are required for a benign phyllodes tumour.
  1. Slit-like spaces may absent in a borderline phyllodes or a malignant phyllodes.
  2. A cellular tumour without features suggestive of malignancy and without slit-like spaces is a cellular fibroadenoma.
     • Some pathologists don't believe in cellular fibroadenoma - they call everything with stromal cellularity a phyllodes tumour.

DDx:

• Fibroadenoma.
• Metaplastic breast carcinoma.
• Primary breast sarcoma.
• Other sarcomas.

Images

• 

  Phyllodes tumour - very low mag. (WC/Nephron)

• 

  Phyllodes tumour - low mag. (WC/Nephron)

Grading

Phyllodes tumours are graded:

• Benign.
• Borderline.
• Malignant.

Grading phyllodes tumours - based on WMSP:

Feature	Benign phyllodes	Borderline phyllodes	Malignant phyllodes
Circumscription	Well	Well	Poor
Stromal overgrowth †	none	none	may be present
Nuclear atypia	mild	mild-to-moderate	moderate-to-marked
Mitoses per 10 HPFs ‡	< 5	5-10	>10
Heterologous elements	+/- benign	+/- benign	+/- malignant
DDx	fibroadenoma	benign phyllodes, malignant phyllodes	metaplastic breast carcinoma, sarcoma

Notes:

• † Stromal overgrowth = epithelial elements absent in one low power field (LPF), defined as x40; LPF is not adequately defined - see LPFitis.
• ‡ HPF is not adequately defined - see HPFitis.

See also

• Breast pathology.