Studies by Danaee et al. (2017) reported that the transmembrane receptor protein, guanylyl cyclase C (GCC), was selectively and specifically overexpressed in CRC cells and thus can potentially be utilized as a specific biomarker to mediate anti-antibody targeted CRC PS uptake and retention within photo-diagnostic and treatment therapies [15,16]. The gene discussed is GUCY2C; the disease is colorectal carcinoma.