Coexisting invasive ductal carcinoma arising within a benign phyllodes tumour

A woman in her 40s presented to the breast clinic with a 2-year history of an enlarging right breast lump. Examination revealed a 10 cm firm mass in the upper outer quadrant of the right breast. MRI and ultrasonography results revealed an 8 cm mass in the right breast and suspicious axillary nodes. Biopsy results of this mass revealed a sclerosed fibroadenoma (B2). Excision of the right breast lump had shown a benign phyllodes tumour, containing an incidental invasive ductal carcinoma and high-grade ductal carcinoma in situ. The patient underwent a right breast cavitectomy and sentinel lymph node biopsy, which revealed no further disease. She received adjuvant radiotherapy, chemotherapy and anti-HER2 treatment, and has remained disease-free at 20-month follow-up. The coexistence of an invasive carcinoma arising within a benign phyllodes tumour is rare. This case report underscores the importance of thoroughly examining excised specimens for phyllodes tumour to exclude malignant components.