Invasive ductal carcinoma arising in a recurrent phyllodes tumor of the breast: a case report.

Background: Invasive ductal carcinoma (IDC) of the breast is the most common subtype of breast cancer, yet its presentation following benign breast lesions such as fibroadenoma or phyllodes tumor is rare. Case presentation: A 38-year-old Iranian woman with a history of hypothyroidism, who underwent IVF and fertility medications, with 4-year history of contralateral fibroadenoma and phyllodes tumor, underwent excision at 2023. During follow-up, the left breast phyllodes tumor recurred and, upon core biopsy, demonstrated high-grade IDC. Axillary fine-needle aspiration revealed metastatic carcinoma. The patient received systemic chemotherapy followed by left mastectomy with axillary lymph node dissection; final pathology confirmed IDC, with negative margins and no residual nodal involvement. Discussion: Carcinoma arising within phyllodes tumor is rare, and careful histopathologic evaluation is essential to identify coexisting or evolving carcinoma. Management should follow standard breast cancer protocols, including axillary evaluation and adjuvant therapy, while ensuring complete excision of the fibroepithelial component. Patient-specific risk factors, such as IVF history and occupational radiation exposure, may contribute to breast oncogenesis and underscore the importance of vigilant surveillance. Conclusion: Patients with prior benign breast tumors, including fibroadenoma and phyllodes tumor, should undergo regular clinical and radiologic follow-up. Early identification of malignant changes enables timely intervention and improves prognosis. This case highlights the need for vigilance even years after excision of benign breast lesions.