lifespan (Figure 1C). These results suggested that deletion of exon 14 indeed results in either loss or abnormal function of the Apc gene product. ApcΔ580/+ mice have median survival of 5 mo of age (Figure 1C), with progressive signs of rectal bleeding and anemia. Similar to the results reported with an independently generated ApcΔ580/+ conditional mouse strain [14], ApcΔ580/+ mice had more than 100 (120 ± 37, n = 11) intestinal tumors at the time of their death (F