CPS1 and hepatocellular carcinoma: To compensate for their low or no expression, we here used a combination of anti-carbamoyl phosphate synthetase 1 (CPS1, a newly identified antigen for Hep Par 1) [24] and anti-P-CK antibodies to allow the detection of all types of HCC CTCs including CPS1+/CK+, CPS1−/CK+ and CPS1+/CK− HCC cells.