Sarcoid-like Reaction in Breast Cancer Tumor Bed and Axillary Lymph Nodes Following Neoadjuvant Chemotherapy: A Case Report.

Although granulomatous change is not commonly seen in breast cancer tumor bed and/or lymph node after neoadjuvant chemotherapy (NCT), they may mimic lymph node metastasis or tumor progression or recurrence. We present a case of diffuse sarcoid-like reaction (SLR) developed in both the breast tumor bed and axillary lymph nodes after NCT. A postmenopausal Hispanic woman presented with a 11.4 cm left breast mass with swollen lymph nodes in her left axilla. A core biopsy of the breast mass was performed, leading to the diagnosis of grade 3 invasive ductal carcinoma. The tumor is negative for estrogen receptor, progesterone receptor, and human epidermal growth factor receoptor-2 overexpression. The patient received NCT with three cycles of doxorubicin and cyclophosphamide, followed by weekly paclitaxel for 12 weeks. After NCT, the tumor in her left breast significantly reduced in size, but the lymph nodes remained swollen. She subsequently underwent left modified radical mastectomy. Histological examination of the treated tumor bed revealed residual invasive tumor with frequent non-caseating granulomatous change. The granulomatous reaction was also seen in several axillary lymph nodes, of which only one had residual metastatic tumor cells. Idiopathic granulomatous mastitis, sarcoidosis, and infective etiologies were excluded based on the patient's medical history, imaging, and histological findings. We report a case of localized SLR in response to NCT in breast cancer tumor bed and axillary lymph nodes. Recognizing this feature is important to avoid misdiagnosis and overtreatment of SLR as residual cancer.