ERBB2 and cancer: By using EVs as the “body’s antigen delivery system” for targeting a novel prodrug 6-chloro-9-nitro-5-oxo-5H-benzo(a)phenoxazine (CNOB)/ChrR6 regimen specifically to HER2 positive cancer, the cytotoxic product of this regimen, 9-Amino-6-chloro-5H-benzo(a)phenoxazine-5-one (MCHB), can be visualized noninvasively in living mice (Fig. 3e) [56–59].