Invasive Ductal Carcinoma Within a Borderline Phyllodes Tumor Associated With Extensive Ductal Carcinoma In Situ: A Case Report

Phyllodes tumors of the breast are rare biphasic fibroepithelial neoplasms that may coexist with breast carcinomas. Herein, we report a case of invasive ductal carcinoma (IDC) within a borderline phyllodes tumor accompanied by extensive ductal carcinoma in situ (DCIS) in the same breast. A 72-year-old woman presented with a palpable lump in the right breast. Mammography showed an oval mass associated with segmental microcalcifications, and breast ultrasound (US) revealed a 2.3 cm oval mass and an associated non-mass lesion. Based on US-guided core needle biopsy, the initial biopsy result of the non-mass lesion suggested DCIS; however, the mass was diagnosed as a fibroepithelial lesion. Preoperative dynamic contrast-enhanced magnetic resonance imaging showed a rim-enhancing oval mass with areas of T2 hyperintensity, accompanied by segmental non-mass enhancement. The mass was highly suspicious for malignancy and was considered imaging-pathology discordant. Subsequently, the patient underwent mastectomy. Histopathological examination of the surgical specimens confirmed a borderline phyllodes tumor with an IDC within the tumor and an extensive intraductal component. The invasive carcinoma component was triple- negative breast cancer. This case highlights the diagnostic challenges of identifying coexisting carcinomas within phyllodes tumors and emphasizes the necessity for increased awareness among radiologists regarding this possibility.