KRAS and carcinoma of esophagus: Although a loss of antisense-transfected cells during clonal expansion has been described, for example, in oesophageal cancer cells with antisense to cyclin D1 (Zhou et al, 1995), no such phenomenon has ever been reported using antisense oligomers or antisense expression vectors against the K-ras gene (Mukhopadhyay et al, 1991; Zhang et al, 1993; Aoki et al, 1995, 1997; Alemany et al, 1996; Kita et al, 1999).