Abstract / Summary
Abstract Background Primary leiomyosarcoma of the breast is an exceptionally rare mesenchymal tumor, constituting less than 1% of all breast malignancies. Its diagnosis is often delayed due to clinical and radiological similarities to more common benign or epithelial breast tumors. Case Presentation A 60-year-old woman presented with a painless, gradually enlarging lump in the retroareolar region of the left breast, 10 years after undergoing lumpectomy for a similar lesion. Imaging revealed a hypoechoic, vascular mass measuring 6.5 × 5.1 cm. Mammography showed a well-defined, dense lesion. A core biopsy indicated benign acini with mild stromal pleomorphism and a low Ki-67 index. The patient underwent modified radical mastectomy. Histopathology revealed a malignant phyllodes tumor with a heterologous component of leiomyosarcoma. Immunohistochemistry showed strong positivity for smooth muscle actin and a Ki-67 index of 7%–8%. The tumor was staged as pT3NxMx. Postoperative chemotherapy was initiated, and the patient tolerated the first cycle well. Clinical Discussion Primary breast leiomyosarcoma is often misdiagnosed due to its rarity and nonspecific presentation. Histopathology and immunohistochemistry are crucial for definitive diagnosis, particularly when arising within a malignant phyllodes tumor. Complete surgical excision with negative margins remains the mainstay of treatment. The benefit of adjuvant therapy is unclear due to limited data, and management must be individualized. Regular follow-up is essential, given the risk of local recurrence and hematogenous metastasis. Conclusion This case highlights the importance of considering rare mesenchymal tumors in patients with recurrent breast lumps. A multidisciplinary approach combining imaging, histopathological evaluation, and individualized treatment planning is critical to optimize outcomes in such rare entities.