Herein, we found that LOXL4 was significantly correlated with breast cell proliferation and migration in vitro and tumor metastasis in vivo. We performed gain- and loss-of-function studies, and provided strong evidence that LOXL4 was a key determinant of breast cancer tumorigenesis and metastasis (Figures 2D-J and 3D-I), in contrast to a previous study showing that LOXL4 was downregulated in breast cancer tissues 42. The gene discussed is LOXL4; the disease is breast cancer.