RESUMO
ABSTRACT: Phyllodes tumor of the breast with malignant transformation to fibrosarcoma of the breast is a rare entity. Breast fibrosarcoma is uncommon, accounting for less than 1% of all breast tumors. Prognosis of fibrosarcoma of the breast is poor. Due to its rarity, survival rates are not defined. A 23-year-old woman presented with a mass in the left breast, and another 48-year-old woman presented with right breast mass. Both patients underwent for surgery. The histological & immunohistochemical examination confirms the diagnosis of a malignant transformation from borderline phyllodes tumor to fibrosarcoma. We concluded that the phyllodes tumor is mostly benign but local recurrence is common. As the tumor progresses toward malignancy, due to the difficulty in the diagnosis of borderline phyllodes tumors, total mastectomy with axillary resection must be recommended.