CCL21 and neoplasm: Specifically, while inhibition of Wnt signaling with the specific inhibitor XAV-939 significantly decreased sphere-forming ability and hence stemness properties in primary PyMT-expressing tumor cells as expected [29], addition of the CCR7 ligand CCL21 to XAV-939 treated cells was sufficient to restore sphere formation to that seen when stimulated with CCL21 alone (Additional File 1: Figure S3), thus demonstrating that the Wnt pathway is not involved in CCR7-mediated regulation of stem cell maintenance.