Malignant Phyllodes Tumour with Heterologous Osteosarcomatous differentiation and Osteoclast-like giant cells: Case Report of an uncommon neoplasm

Abstract

Background: Phyllodes tumour (PT), an uncommon fibroepithelial neoplasm accounts for less than 1% of all primary tumours 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 aetiology. Preoperative core needle biopsy raised the possibility of a phyllodes tumour versus giant cell tumour. Wide local excision was performed to confirm the diagnosis which revealed the presence of a biphasic tumour with 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 tumour 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 with careful histopathological examination. Wide local excision with close surveillance is crucial for timely detection of tumour recurrence and metastasis.