A 48-year-old woman with mucinous carcinoma in the left breast.Axillary US demonstrating suspicious lymph nodes with cortical thickening (arrows) and effacement of the fatty hilum (crosses). The patient received a third dose of the BNT162b2 vaccine in the left deltoid muscle four days before the preoperative axillary US. Ultrasonography-guided fine-needle aspiration of the lymph nodes was negative for malignant cells. Left breast-conserving surgery and sentinel lymph node biopsy were performed, and final pathology revealed no axillary lymph node metastasis. US = ultrasound