All mammary tumors that showed retention of the wild-type Apc allele were analyzed by IVTT, and truncated Apc products were detected in 19 of 20 (95%) K14-Cre; ApcCKO/+ and all 3 (100%) ApcΔ580/+ mammary tumors, as well as in a single WAP-Cre; ApcCKO/+ mammary tumor that did not show loss of the wild-type allele (Table 2). This evidence concerns the gene APC and breast cancer.