RFP Reporter Cell Line-4T1 is a polyclonal population which is constructed by lentivirus transduction, followed by stable cell selection. This cell line stably expresses RFP and puromycin resistance gene driven by spleen focus-forming virus (SFFV) promoter. It is an ideal positive control for use in fluorescence assays. In addition, 4T1 cells form tumors post implantation into immunocompromised or syngenic mice. The in vivo growth of these tumors can be monitored using optical imaging for RFP fluorescence.