CEACAM5 and adenocarcinoma: Zhang et al. [30] studied the efficiency of the double system cytosine deaminase (CD) and thymidine kinase (TK) targeted by CEA promoter in CEA positive human gastric cancer cell line (SGC7901) versus a CEA negative human adenocarcinoma cell line (HeLa), showing a greater growth inhibition in SGC7901 (89.8%) than in HeLa line cell (2%).