CCR4 and melanoma: Moreover, “brain‐derived soluble factors” could upregulate CCR4 expression in melanoma cells and facilitate the migration of brain‐metastasizing melanoma cells specifically.92 Recently, a crucial relationship between several altered C‐C motif receptor 4 (CCR4) ligands, including C‐C motif ligand 4/17/22 (CCL4/17/22) and poor clinical outcomes have been observed.