Excisional biopsy specimen from a 52 year old women with a 3.1 cm mass
Diagnosis: Malignant phyllodes tumor with liposarcomatous elements
Discussion: Features of malignant phyllodes tumor include stromal overgrowth (defined as a 4x field composed exclusively of stroma), stromal atypia, and mitotic activity. The low power photomicrograph suggests an irregular interface with fat, but in fact the adipose tissue is actually part of the phyllodes tumor, and qualifies as stromal overgrowth. Numerous lipoblasts are evident under high power. Margin adequacy is the most important predictor of local recurrence. Given the low grade nature of this phyllodes tumor, a good outcome is expected following adequate surgical excision.