Complete disappearance of ductal carcinoma

Introduction and importance: Ductal carcinoma Case presentation: A 51-year-old woman presented with a right breast mass, clustered microcalcifications, biopsy-proven axillary nodal metastasis, and a suspicious subclavicular node. Core needle biopsy of the breast showed high-grade DCIS with focal suspicious microinvasion and an HR-negative/HER2-positive phenotype. She received anthracycline- and taxane-based NAT with anti-HER2 therapy, followed by a right modified radical mastectomy and nodal dissection. Final pathology demonstrated no residual invasive carcinoma, no residual DCIS in the breast, and no residual nodal disease, consistent with a pathological complete response. Clinical discussion: This finding should not be interpreted as definitive evidence that DCIS itself is chemosensitive. In the present case, the disappearance of the DCIS component may have resulted from a bystander effect after the disruption of the ductal barrier by microinvasive or unsampled invasive disease. In addition, persistent post-NAT microcalcifications on mammography did not indicate viable residual tumor, highlighting the risk of overtreatment when the surgical extent is determined primarily by residual calcifications. Conclusion: This case underscores three clinically relevant points: nodal metastasis in biopsy-diagnosed DCIS/ductal carcinoma