[A Case of Sarcoid-Like Reaction That Was Difficult to Distinguish from Breast Cancer Relapse]

An elderly woman in her 80s with a medical history of rheumatoid arthritis and chronic hepatitis B was diagnosed with Stage Ⅳ, ER-negative, HER2-positive invasive ductal carcinoma of the left breast, with mediastinal lymph node metastases. She received chemotherapy combined with anti-HER2 therapy and achieved a complete remission after 12 months. Three years and 7 months later, FDG-PET/CT revealed enlargement of the left axillary lymph nodes, and they were suggested as recurrences. Radiotherapy was administered, resulting in temporary reduction in lymph node size. However, 10 months later, the lymph nodes re-enlarged and were subsequently surgically resected. Histopathological examination revealed that they were non-caseating granulomas without any evidence of malignancy, consistent with a diagnosis of sarcoid-like reaction. The patient has been followed up postoperatively without recurrence for 12 months.