Malignant Phyllodes Tumor with Heterologous Osteosarcomatous Differentiation and Osteoclast-like Giant Cells: A Case Report of an Uncommon Neoplasm.

Background: Phyllodes tumor (PT), an uncommon fibroepithelial neoplasm accounts for less than 1% of all primary tumors of the breast. MPT with osseous differentiation often gets misdiagnosed on imaging as benign giant calcifications resulting in treatment delay. We describe a rare case of MPT with heterologous osteosarcomatous differentiation and osteoclast-like giant cells and review the literature to discuss clinical-radiological findings, differential diagnosis and treatment options. Case Presentation: A 34-year-old female presented with a right breast lump. Mammography showed a high-density irregular mass with amorphous dense calcification, suggesting neoplastic etiology. Preoperative core needle biopsy raised the possibility of a phyllodes tumor versus a giant cell tumor. A wide local excision was performed to confirm the diagnosis, which revealed the presence of a biphasic tumor with an osteoid-like matrix and numerous osteoclastic giant cells. Immunohistochemistry was used to rule out metaplastic carcinoma or carcinosarcoma. The stromal cells were negative for panCK and P63 and positive for vimentin, CD10 and BCL-2. The osseous component was positive for Osteonectin and SATB2. Thus, a final diagnosis of malignant phyllodes tumor with heterologous osteosarcomatous differentiation and osteoclast-like giant cells was made. Conclusion: MPT with osteosarcomatous differentiation is a rare and challenging entity associated with a poor clinical outcome. Accurate diagnosis requires a multidisciplinary approach involving breast surgeons, pathologists, and radiologists, along with careful histopathological examination. Wide local excision with close surveillance is crucial for the timely detection of tumour recurrence and metastasis. [ABSTRACT FROM AUTHOR]