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Phyllodes Tumor with Osteosarcomatous Differentiation: A Comparative Immunohistochemical Study between Epithelial and Mesenchymal Cells

Aims and background Phyllodes tumor of the breast with osteosarcomatous differentiation is rare and very little is known about its molecular profile. Methods and study design An immunohistochemical panel with 37 primary antibodies including cytokeratins, mesenchymal markers, key regulators of the cell cycle, oncogenes, apoptosis-related proteins, metalloproteinases and their inhibitors was performed on a formalin-fixed paraffin-embedded sample of phyllodes tumor with osteosarcomatous differentiation in a 49-year-old woman. Results Antiapoptotic stimuli (survivin) predominated in sarcomatous cells. Antiproteolytic stimuli (TIMP-1, TIMP-2 and PAI) were preponderant in all cells, a surprising fact in view of the aggressiveness of the neoplasm. The immunoprofile of the osteoblastic and stromal cells was quite similar, except for c-erbB-3, c-myc, cyclin D1 and p21. Both exhibited positive cells for actin, MyoD1 and GFAP. Conclusions Our results suggest that this osteosarcoma may have originated from metaplasia of stromal cells that underwent a malignant change.