Phyllodes tumour is predominantly seen in middle-aged women, arising from periductal-stroma with leaf-like growth pattern on histology and a large, rapidly growing mass with lobulated borders on mammography.
- Leaf-like stromal projections into epithelium-lined clefts. Clefts form distinctive cystic spaces.
Description
Phyllodes (Greek: leaf-like) tumours are rare fibroepithelial breast tumours characterised by a dominant stromal component. They comprise a spectrum ranging from benign to malignant but are locally aggressive.
Pathogenesis
Phyllodes tumours arise from the periductal stroma of the breast. These tumours have a hypercellular stromal component which can demonstrate varying degrees of atypia. The pathogenesis is not completely understood but it is thought to involve mutations in genes such as TP53, RB1 and MED12.
Subtypes
Phyllodes tumours are divided into three histological subtypes based on stromal cellularity, atypia, mitotic activity and border appearance, each increasing in rate of recurrence:
- Benign (60%): Characterised by mild stromal cellularity and minimal atypia (can occur in girls under 10, but usually seen >10 years.
- Borderline (20%): Moderate stromal cellularity and atypia, with increased mitotic activity.
- Malignant (20%): High stromal cellularity, marked atypia, and increased mitotic activity with infiltrative borders.
Epidemiology, Risk Factors & Associations
- Peak incidence in the fifth decade of life
- History of fibroadenoma (5% risk of developing phyllodes tumour)
- No significant associations with family history or reproductive risk factors
Clinical Features
Phyllodes tumours typically present as a large, rapidly enlarging, painless breast mass. Less commonly, there can be skin changes such as erythema or breast asymmetry.
Complications
Risk of malignant transformation is tied to the histological subtype: benign (1%), borderline (5-10%), malignant (20-30%). Metastatic potential primarily to lungs and bones is mainly seen in malignant subtype.
Pathological Features
Histopathology
- Macroscopic: Large, rounded, well-circumscribed mass with bulging cut surface. It has leaf-like excrescences and intervening cystic spaces.
- Microscopic: Overgrowth of stroma relative to epithelium. Depending on the grade, stromal cellularity, cytologic atypia, and mitotic activity increase. Tumour can resemble a giant fibroadenoma.
Serology
No specific serological markers.
Radiological Features
General Features
- Heterogenous, solid-appearing mass.
- Can mimic a fibroadenoma.
- Benign, borderline and malignant subtypes may be difficult to differentiate based on imaging.
- Rapidly growing mass with lobulated or irregular margins, therefore can present as a large mass.
- Typically, no calcifications (seen in 10% cases)
- Heterogeneous enhancement with areas of low signal intensity on T2-weighted images due to high cellularity and stromal overgrowth.
Mammography
- Well-defined ovoid or smoothly lobulated mass which can be large at presentation
Ultrasound
- Generally non-specific and can mimic a fibroadenoma
- B-mode: Heterogeneous, predominantly hypoechoic mass with lobulated or irregular margins with posterior acoustic shadowing. Contains multiple, round or cleft-like cystic spaces.
- Doppler: Solid components of the tumour shows vascularity.
MRI
- Well-defined margins, round or lobulated mass
- Internal septations (non-enhancing) and heterogeneity are suggestive but not definitive for phyllodes tumours
- T1: Usually low or isotense to adjacent parenchyma. Bright T1 signal (with corresponding T2 hypointensity) may reflect intratumoural haemorrhage, particularly in large or malignant phyllodes tumours.
- T2: More commonly low or intermediate signal. Hyperintensity can be seen in 33%. Internal cysts may be seen. Peritumour hyperintensity may be seen due to interstitial fluid accumulation or lymphatic obstruction from rapid tumour growth.
- Gd+: Solid areas enhance. Three enhancement patterns:
- Type 1: Slow initial enhancement with persistent delayed phase, suggestive of benignity, seen in 66.7%
- Type 2: Rapid initial enhancement with plateau phase, seen in 12.5%
- Type 3: Rapid initial enhancement with wash-out, seen in 20.8%—a pattern more typically associated with malignancy
- 33.3% of phyllodes tumours demonstrated a suspicious enhancement curve (type 2 or 3), despite histologically benign features.1
Grading and Staging
Grading is based on the histological appearance as benign, borderline, or malignant. There is no specific staging system for phyllodes tumours.
Diagnosis
Imaging cannot distinguish between benign and malignant phyllodes tumour. Core needle biopsy for histopathological examination is typically performed, although the definitive diagnosis is usually established after excision biopsy. Core biopsy has moderate sensitivity due to tumour heterogenity causing inadequate sampling. Fine needle aspiration is inaccurate.
Prognosis
Whilst the majority of phyllodes tumours are benign, approximately 25% are malignant and 20% of those may metastasise. Incomplete resection results in recurrence.
Differential Diagnosis
- Fibroadenoma: Substantial imaging overlap exists, particularly in small lesions. Characterised by well-circumscribed, hypoechoic mass with posterior acoustic enhancement on ultrasound. Histologically resembles a phyllodes tumour with both epithelial and stromal components seen, however, lacks rapid growth associated with phyllodes tumour. Calcification is more common. Peritumoural oedema usually not present.
- Breast carcinoma: Irregular shape, spiculated margins, posterior shadowing on ultrasound, and presence of microcalcifications on mammography can suggest this diagnosis.
Management
Surgical resection with clear margins is the mainstay of treatment. The role of adjuvant therapy is still uncertain and typically reserved for high-risk or recurrent cases. Each recurrence may show grade deterioration.
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