Clinically, GPA33 expression has been observed in over 95% of colorectal cancers (CRCs) and associated metastases (Garinchesa et al., 1996), an observation that has underpinned an ongoing and concerted effort to use radionuclide-bound murine (Welt et al., 1994, 1990) and humanised (huA33 mAb) monoclonal antibodies to target GPA33-expressing tumours (Ciprotti et al., 2014; Infante et al., 2013; Scott et al., 2005; Welt et al., 2003, 1996). The gene discussed is GPA33; the disease is colorectal cancer.