We investigate the usefulness of the CT antigens SPA17 (sperm protein-17 [SP-17]), IGF2BP3 (insulin-like growth factor-II mRNA-binding protein 3 [IMP-3]), and transmembrane protein with epidermal growth factor (EGF)-like and two follistatin-like domains 1 (TMEFF1) as potential MCC biomarkers and evaluate their possible utility in immunotherapy and molecularly targeted image-guided treatment.