Regional Metastases, Artifacts, and Mimics in Axillary Lymph Nodes

Axillary lymph node status is an important prognostic factor in breast cancer. In most patients, sentinel lymph node biopsy has replaced axillary dissection because it decreases morbidity and permits accurate staging and local control. The increased histologic scrutiny of sentinel lymph nodes and consideration of drainage phenomena has led to a heightened awareness and detection of previously described but rare findings. These include false-positive findings such as benign heterotopic glands, transported epithelial cells, nevus cell aggregates, megakaryocytes, multinucleated giant cells, silicone lymphadenopathy, and histiocytes, all of which may mimic metastatic carcinoma. Conversely, degenerated or treated cancer cells can appear artifactually negative, mimicking histiocytes. In addition, many artifactual changes in lymph nodes are due to the use of immunohistochemistry. Overlapping staining with dendritic cells, histiocytes, and plasma cells can be misinterpreted as positive. Most of these issues can be resolved by comparing the lymph node findings with the primary tumor.