Utilisation of the CEA promoter in an adenovirus vector for cytosine deaminase (CD) gene expression improves the selectivity of 5′-deoxy-5-fluorocytidine (5-DFCR)/5-fluorouracil (5-FU) conversion in CEA-expressing tumours (Richards et al, 1995a; Lan et al, 1996a). The gene discussed is CEACAM5; the disease is neoplasm.