CXCL12 and skin neoplasm: On the other hand, cytotoxic T cells expressing CXCR4 could migrate into melanoma in response to low concentrations of CXCL12 whereas a high concentration of this chemokine caused T cells to undergo fugetaxis (44, 71–73), highlighting a complex concentration-dependent role for CXCL12 at least in this form of skin cancer.