24th May 2025

Phyllodes Tumour

Phyllodes tumours are an uncommon breast neoplasm, accounting for around 1% of all breast tumours. Whilst they can affect women of any age, Phyllodes tumours are more commonly found in premenopausal women between the ages of 40 and 50 years. Akin to a fibroadenoma in their appearance, they are characterised by a fibroepithelial proliferation, with a potential to undergo malignant transformation.

Clinical examination usually reveals a smooth, multinodular, mobile, painless breast mass with rapid growth, averaging 3 to 5cm in size at presentation. Larger tumours can distort the overlying skin, resulting in a shiny, stretched appearance. Palpable axillary lymphadenopathy may also be present in as many as 20% of cases, though the underlying pathology is usually reactive in nature, as opposed to metastatic involvement.

Phyllodes tumours usually appear as a well circumscribed, round-to-oval or lobulated lesion with smooth margins on mammography. A radiolucent halo may also be seen. Ultrasound typically reveals an inhomogeneous, solid appearing mass, largely indistinguishable from a fibroadenoma. As such, imaging alone is insufficient for diagnosis and histological evaluation is necessitated.

Core biopsy is the preferred modality for histological assessment, as fine needle aspiration (FNA) is associated with a high false negative rate and low overall diagnostic accuracy. Histology shows a biphasic proliferation of both epithelial and stromal elements, with an overarching ‘leaf-like’ architecture. Due to the heterogeneity of the tumour, up to 30% of core biopsy specimens may also provide a false negative result and therefore, surgical excision may be required. This may involve breast conserving surgery in the form of a wide-local excision, or a full mastectomy. 

Phyllodes tumours are graded on their histological appearance, which incorporates the degree of cellular atypia, stromal overgrowth and number of mitoses, amongst other features. The vast majority of tumours will fall into the benign category, whilst more atypical tumours may be graded as borderline or malignant. Irrespective of the grading, Phyllodes tumours have a propensity to recur and therefore, follow-up is recommended. However, these tumours are not associated with an increased risk of invasive breast cancer.