To investigate the cellular localization of Arg within the primary tumor, we examined tissue sections of orthotopic xenograft tumors that were generated from MDA-MB-231 cells expressing Arg-YFP, cortactin-TagRFP, and MMP Sense, a protease-activatable fluorescent in vivo imaging agent that is optically silent upon injection and produces a fluorescent signal following cleavage by MMPs. Here, CTTN is linked to neoplasm.