Supplementary Material for: Necrosis of a Metastatic Axillary Lymph Node in Breast Cancer Possibly Induced by Fine Needle Aspiration Cytology: A Case Report

Introduction: Axillary lymph node metastasis is a major prognostic factor for breast cancer. In rare cases, metastatic lesions may undergo necrosis.
Case Presentation: A 69-year-old woman with a history of rheumatoid arthritis and ovarian tumor surgery was diagnosed with right-sided breast cancer (cT1N1M0) following abnormal screening mammography. Core needle biopsy revealed invasive ductal carcinoma (estrogen receptor: > 95%, progesterone receptor: < 1%, human epidermal growth factor receptor 2: 2+ [fluorescence in situ hybridization-negative], MIB-1: 18%). Fine needle aspiration (FNA) cytology of an enlarged axillary lymph node confirmed metastasis. Mastectomy and axillary dissection were performed approximately 3 months after the FNA procedure without preoperative treatment, suggesting a temporal relationship between aspiration and subsequent necrosis. Histopathological analysis revealed no viable cancer cells in the lymph nodes but uniform eosinophilic necrosis with partial epithelial-like structures in one node. Immunohistochemistry showed positivity for epithelial membrane antigen, AE1/AE3, estrogen receptor, and GATA3, and histiocytes surrounding the necrotic area were positive for cluster of differentiation 68 and -163. These findings suggested that the metastatic carcinoma had undergone necrosis, likely triggered by FNA. The Oncotype DX score was 33; however, the patient chose endocrine therapy alone. No recurrence has been observed at the time of writing, 18 months after surgery.
Conclusion: This case highlights a rare instance of necrosis in a metastatic lymph node, possibly induced by FNA. Immunohistochemistry is essential to confirm the diagnosis and avoid misinterpretation as a granulomatous or infectious process.