TKT and colorectal neoplasm: In fact, Okabe et al. [34] have demonstrated that the CEA promoter in an adenovirus expressing the TK gene was able to improve its antitumor activity in mice bearing colorectal tumors from RCM-1 CEA-positive cells and to reduce the number of liver metastases (after 42 days of treatment) in relation to an untreated group of mice.