Ectopic Breast Cancer Arising within an Axillary Lymph Node.

We report our experience with the diagnosis and treatment of an ectopic breast cancer arising within an axillary lymph node. The patient was a 65-year-old woman diagnosed breast cancer and axillary lymph node metastasis. We performed a partial mastectomy and axillary lymph node dissection. Postoperative pathology revealed no malignant lesions in the breast; however, a nodule in one of axillary lymph nodes had mixed benign and malignant components, leading to a diagnosis of invasive ductal carcinoma derived from ectopic mammary tissue. This case represents a very rare form of breast cancer, and the malignancy was difficult to distinguish from metastasis.