A Case of Breast Cancer with Cystic Axillary Lymph Node Metastasis.

INTRODUCTION: Encapsulated papillary carcinoma (EPC) is a relatively rare form of breast cancer and is often low grade. Even in cases of EPC with invasion, it rarely metastasizes. We herein report a case of EPC with invasion that presented with a cystic axillary lymph node metastasis that was highly characteristic on imaging. CASE PRESENTATION: A 73-year-old woman presented with a mass in the right breast. Mammogram showed linear calcifications in the middle-outer region of the right breast and a lobulated mass in the lower region. Ultrasound revealed a cystic mass with extensive fluid formation in the breast and a hypoechoic mass with indistinct borders. Numerous cystic enlarged lymph nodes, similar in appearance to the intramammary mass, were detected in the ipsilateral axilla. Contrast-enhanced MRI also revealed multiple cystic enlarged lymph nodes in the axilla. Cytology of the axillary lymph nodes was suggestive of metastasis. The patient underwent a right mastectomy and axillary dissection, and histopathological examination confirmed a diagnosis of EPC with invasion (pT2N2aM0, Stage IIIA). The metastatic axillary lymph nodes contained cystic structures with papillary proliferation, closely resembling the primary EPC lesion. The patient was treated postoperatively with endocrine therapy alone, and to date, no recurrence has been observed 18 months after surgery. CONCLUSIONS: This case highlights a rare instance of EPC with invasion presenting as cystic lymph node metastases, which was strikingly evident on imaging. Awareness of this unique metastatic pattern may be useful in daily clinical practice for facilitating accurate diagnosis and appropriate management of EPC.