Intraductal Papilloma Originating From Ectopic Breast Tissue Within a Sentinel Lymph Node Can Mimic Metastatic Carcinoma: A Case Report.

The presence of ectopic breast tissue within axillary lymph nodes is a benign condition that must be distinguished from primary or metastatic carcinoma. Here, we present a patient who was previously diagnosed with invasive breast cancer in her right breast and intraductal papilloma in her left breast, presenting with a new enlargement in her left axilla during follow-up. This enlargement mimicking carcinoma metastasis underwent a frozen section followed by excision of axillary lymph nodes. A histological examination of the excised axillary lymph node revealed intraductal papilloma, characterized by papillary and tubular structures lined with luminal cuboidal cells within the lymph node. Immunohistochemical analysis confirmed the diagnosis of ectopic intraductal papilloma, demonstrating positive staining for estrogen receptor (ER), progesterone receptor (PR), GATA3, and p63, with heterogeneous expression of ER, PR, and KRT5/6. Although it is extremely rare, this lesion highlights the importance of considering this phenomenon in differential diagnoses, as benign proliferative changes in ectopic breast tissue can mimic malignancy, necessitating careful histopathological and immunohistochemical evaluation.