U937/STAT3 Reporter (Luc) cells are derived from the human pro-monocytic cell line U937 by stably integration of a STAT3 firefly luciferase reporter construct. U937 cells are able to differentiate into either dendritic cells or macrophages, depending on the surrounding signals. U937 cells are widely used for studies of monocyte/macrophage differentiation, the macrophage-tumor cell interaction and anti-cancer drug screening. U937/STAT3 Reporter (Luc) cells stably express firefly luciferase under the control of the STAT3 response elements, can be used for monitoring the activity of STAT3 signaling pathway.