CCR7 and breast carcinoma: In 4T1 tumor-bearing mice, NADPH oxidase 4 (Nox4) increases tumor lymphangiogenesis via reactive oxygen species (ROS)/extracellular signal-regulated kinase (ERK)/chemokine CC-ligand 21 (CCL21) pathway and attracts CC chemokine receptor 7 (CCR7)-positive breast cancer cells to entry lymphatic vessels and spread to distant organs [91].