Rescue in Apchet mice occurs through Cre-mediated truncation of the fourth Armadillo repeat (bin B, position 580), providing a second hit in cells with ENU-induced single-allele mutations of Apc. When applying the second hit 30 days after ENU treatment, the mean (s.d.)tumour multiplicity was 109 (32) compared with 967 (267) in the primed condition—a 90% reduction. This evidence concerns the gene APC and neoplasm.