Clinical history: A 51 year old woman presented with a breast mass. Excisional biopsy performed.
What is the most probable diagnosis?
Borderline Phyllodes Tumor
Clinically, Phyllodes tumor (PT) usually presents as a solitary, firm mass that may demonstrate rapid growth and may be larger than 4 cm, helping to distinguish them from fibroadenomas. The median age at presentation is 45 but ranges from 10-86.
Grossly, the tumors are well circumscribed but not encapsulated. When cut, the tumor is firm, grey and bulging, often with leaf-like architecture due to the many interlacing clefts in the tumor. Degenerative foci with necrosis, infarction or hemorrhage may be present.
The periductal stroma is the site of origin of the Phyllodes tumor. Classically, the tumor resembles an intracanalicular fibroadenoma with increased stromal cellularity. The ductal epithelium lining the clefts may be hyperplastic and occasionally demonstrates atypia. The stroma is key to distinguishing PT from fibroadenoma. In PT the stromal cellularity is generally increased and is often densest adjacent to the ductal epithelium.
PTs are subclassified into benign, borderline and malignant as determined by the stromal characteristics. The reason for the subclassification is that benign PT do not metastasize and rarely recur after surgical excision whereas the malignant PT have potential for both metastasis and local recurrence. Benign PT is characterized by a low mitotic rate (<2/10 HPF) with only modest to marked stromal cellular overgrowth with mild cytological pleomorphism and well defined borders. Malignant PT is mitotically active with >5 mitoses per 10 HPF. The stroma is hypercellular with pleomorphism and the tumoral border is frequently infiltrative. The borderline PT may have well defined or invasive borders with an intermediate stromal cellularity that is frequently unevenly distributed. The mitotic rate of borderline tumors is 2-5/10 HPF. Cartillaginous, osseous and lipomatous metaplasia may be seen in any of the classes but in the malignant subtype, there may be sarcomatous features to the metaplastic stroma.
The tumors are managed by local excision. Wide local excision is preferred for decreasing the frequency of recurrence, particularly for tumors with infiltrative borders. Malignant PT may metastasize and the most common sites of metastases are lungs, bone and heart.