Iatrogenically false positive sentinel lymph nodes in breast cancer: Methods of recognition and evaluation

With the introduction of sentinel lymph node (SLN) biopsy as a standard procedure for staging clinically node negative breast cancer patients, meticulous pathologic evaluation of SLNs by serial sections and/or immunohistochemistry for cytokeratins has become commonplace in order to detect small volume metastases (isolated tumor cells and micrometastases). This practice has also brought to the fore the concept of iatrogenically false positive sentinel nodes secondary to epithelial displacement produced largely by preoperative needling procedures. While this concept is well described in the clinical and pathologic literature, it is, in our experience, still under-recognized, with such lymph nodes frequently incorrectly diagnosed as harboring true metastases, possibly resulting in unwarranted further surgery and/or chemotherapy. This review discusses the concept of displaced epithelium in the histologic evaluation of breast surgical specimens and provides a stepwise approach to the correct identification of iatrogenically transported displaced epithelial cells in sentinel lymph nodes.