Metaplastic breast carcinoma is a rare subtype of invasive breast carcinoma. Metaplastic carcinoma with osseous differentiation is exceptionally uncommon. Because of the heterogenous microscopy of the lesion, various clinical and radiological features are observed, leading to diagnostic difficulty. Herein, we present a case of a 43-year-old female with a recurrent breast lump, who was clinically diagnosed as a phyllodes tumor. However, histopathological examination revealed metaplastic carcinoma with extensive osseous differentiation.