Is It Contralateral Axillary Metastasis or Occult Breast Cancer?: A Confusing Case Report.

We report the case of a 43-year-old woman with primary left breast cancer presenting metastatic lymphadenopathy in the contralateral axilla. This patient represents a diagnostic and therapeutic challenge because primary breast cancer, occult contralateral breast cancer, and extra-mammary primary lesion can all be the source of the contralateral axillary metastasis. Left breast-conserving surgery, left sentinel lymph node biopsy, right breast mass excision, and right axillary lymph node dissection were performed. Immunohistochemical analysis revealed that the left breast cancer specimen was positive for estrogen receptor (ER) and progesterone receptor (PR), but negative for human epidermal growth factor receptor 2 (HER2). In contrast, the right axillary lymphadenopathy specimen was negative for ER and PR, but positive for HER2. Further investigation revealed no evidence of occult primary cancers or extra-mammary tumors. After surgical intervention, the patient was treated with adjuvant chemotherapy, adjuvant radiation therapy, and targeted therapy with trastuzumab. Two years after diagnosis, she is free of disease and presently being treated with tamoxifen.