In the human colorectal carcinoma with the CIN phenotype, loss of heterozygosity (LOH) at loci on chromosomes 5q, 17p, and/or 18q is frequent, while CPC;Apc mice carrying constitutional, heterozygous, inactivating mutations in the Apc gene have shown that the wild-type Apc allele is inactivated by LOH, demonstrating that CIN contributes to tumor progression. This evidence concerns the gene APC and cervical squamous intraepithelial neoplasia.