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WHO Classification of Tumours
Phyllodes tumor, borderline
Breast


Definition

Phyllodes tumours (PTs) constitute one of the two major categories of fibroepithelial tumours of the breast (the other being fibroadenomas ). Fibroepithelial breast tumours are biphasic lesions composed of an epithelial and a mesenchymal (stromal) component. The latter is quantitatively predominant and determines the overall appearance of the lesion.
Histologically, phyllodes tumours are characterized by double layers of epithelial and myoepithelial cells arranged in clefts surrounded by a hypercellular mesenchymal component which is typically arranged in leaf-like structures. The characteristics of the stromal component may vary from bland to overtly sarcomatous. PT typically presents as a firm, painless, well circumscribed, rounded mass with an average size of 4.5 cm. Multifocal or bilateral lesions are uncommon. Imaging reveals clefts or cysts and sometimes coarse calcifications. Large lesions may show haemorrhage or necrosis. PTs may arise de novo or from fibroadenomas.
Phyllodes tumours are rare. In Western countries, they account for 0.3-1% of primary tumours and for 2.5% of fibroepithelial tumours of the breast; the majority of patients are middle-aged women with an average age of 40-50 years (rare cases have been reported in men). In Asia, PTs seem to occur more frequently and in younger patients (average age 25-30 years)

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Chua CL, Thomas A, Ng BK (1988)
Cystosarcoma phyllodes--Asian variations.
Aust N Z J Surg 58: 301-5



. The majority of PTs are benign . Borderline and malignant cases are less frequent. The tumour shows a tendency to recur and occasionally metastasizes to internal organs, most commonly to the lungs and the skeleton. Axillary lymph node metastases are rare
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Tavassoli FA, Devilee P (Eds.)
World Health Organization Classification of Tumours. Pathology and Genetics of Tumours of the Breast and Female Genital Organs.
3rd Edition
IARC Press: Lyon 2003



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The morphological characteristics of > borderline phyllodes tumours lie between those of benign and malignant PTs. The stromal sarcomatous changes are of low grade and are often reminiscent of low-grade fibrosarcomas

Click for details
Tavassoli FA, Devilee P (Eds.)
World Health Organization Classification of Tumours. Pathology and Genetics of Tumours of the Breast and Female Genital Organs.
3rd Edition
IARC Press: Lyon 2003



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