Mice lacking CCR7, CCL19 or CCL21 expression due to homozygous deletion (CCR7−/− or CCL19−/− mice) [13,22] or the paucity of lymph node (plt/plt) mouse, in which spontaneous mutations led to the loss of a functional CCL19 and CCL21-ser genes, although the second CCL21 gene, CCL21-leu is functional [25], provide tools for studying the roles of each ligand or receptor in the metastasis of cancer or during an immune response. The gene discussed is CCR7; the disease is cancer.