A false positive for metastatic lymph nodes in the axillary region of a breast cancer patient following mastectomy

Recent advanced imaging modalities such as positron emission tomography (PET) detect malignancies using 2-[18F]-fluoro-2-deoxy-d-glucose (18-FDG) with high accuracy, and they contribute to decisions regarding diagnosis, staging, recurrence, and treatment response. Here, we report a case of false-positive metastatic lymph nodes that were diagnosed by PET/CT and ultrasonography in a 48-year-old breast cancer patient who had undergone mastectomy. The tumors, which were oval shaped and resembled lymph nodes, were detected by ultrasonography. PET/CT revealed high uptake of 18-FDG in the tumors. To investigate the proposed recurrence and to re-evaluate the biology of the recurrent tumors, a tumor was removed from the brachial plexus of the patient. Histological findings revealed it to be a schwannoma. All imaging modalities including PET/CT failed to distinguish benign tumors from metastatic lymph nodes in the brachial plexus. After resection of the schwannomas, the patient complained of a slight motor disorder of the second finger on the right hand. Hence, it is important to consider a false-positive case of lymph node metastasis in a breast cancer patient following mastectomy.