Rare Presentation of Papillary Carcinoma Within a Sentinel Lymph Node in a Patient With Ductal Carcinoma in Situ of the Breast: A Challenging but Useful Case Report Discussion Regarding Displacement or True Metastasis?

Papillary carcinoma of the breast is a rare histologic subtype of invasive breast cancer. In contrast, ductal carcinoma in situ (DCIS) is a noninvasive, nonobligate precursor to invasive mammary carcinoma, confined within the terminal duct lobular unit of the breast and surrounded by an intact myoepithelial cell layer at the stromal/epithelial interface. We present an unusual case in which a patient with only DCIS of the breast exhibited papillary carcinoma within a sentinel lymph node, leading to questions about the origin of the lymph node lesion—whether it represents a true metastasis or iatrogenic displacement during diagnostic procedures. This case underscores the diagnostic challenges and clinical implications associated with such rare presentations.