Impact of CD44+CD24- cells on non-sentinel axillary lymph node metastases in sentinel node-positive breast cancer

Although complete axillary lymph node dissection (ALND) is the standard for evaluating axillary status after the identification of a positive sentinel lymph node (SLN) in breast cancer; approximately 40-60% of SLN-positive patients have negative non-SLN. In this study, to explore putative breast cancer stem cells with CD44+CD24- in the SLN, we retrospectively analyzed the expression of CD44+CD24- on metastatic tumor cells within SLNs as a predictive factor for positive non-SLNs (NSLNs). We tested 271 patients for SLNs using serial sectioning with cytokeratin immunohistochemistry (IHC) and hematoxylin-eosin staining and identified 67 patients who had a positive SLN biopsy and complete ALND. CD44 and CD24 expression was detected using double-staining IHC. Twenty-eight (41.8%) out of 67 patients had positive NSLN metastases. Seven positive SLNs with micrometastases were not available for the evaluation of CD24 and CD44 expression. Out of the remaining 60 patients, 19 (31.7%), 44 (73.83%) and 37 (61.7%) patients had CD24+, CD44+ and CD44+CD24- metastatic tumor cells in SLNs, respectively. Positive NSLN metastasis was significantly associated with the primary tumor size (P=0.004), CD24- expression (P=0.04), CD44+ expression (P=0.01) and CD44+CD24- expression (P=0.02). This report provides the first evidence of the existence of a putative stem-like phenotype within the SLN, which is significantly associated with positive NSLN in early breast cancer patients.