A Rare Case of Mucinous Carcinoma Arising in Association with an Intraductal Papilloma

INTRODUCTION: Intraductal papilloma (IDP) is a benign breast lesion that accounts for 3%-6% of core biopsy diagnoses. It is considered a high-risk precursor due to its association with atypia, ductal carcinoma in situ, and invasive carcinoma. Although IDP-NOS (not otherwise specified) rarely progresses to invasive cancer, IDP with atypia carries a higher risk of malignant transformation. CASE PRESENTATION: A 57-year-old woman presented with a mass in the left breast. Mammography revealed a microlobulated mass, and ultrasonography showed a well-defined, coarse isoechoic mass measuring 26 mm with a disrupted anterior border. MRI revealed a high T2 signal outside the center of the tumor, with early enhancement and a plateau phase. Based on these imaging findings, mucinous carcinoma was suspected; a core needle biopsy revealed both mucinous carcinoma and ductal carcinoma with a mucocele-like lesion. The patient subsequently underwent a total mastectomy and sentinel lymph node biopsy for cT2N0 breast cancer. The surgical specimen revealed a mucinous carcinoma spreading around the papilloma, with a distinct transition zone from papilloma to mucinous carcinoma. CONCLUSIONS: This case suggests that mucinous carcinoma may arise from an intraductal papilloma, emphasizing the importance of appropriate clinical follow-up.