We have previously reported frequent (>40%) EPHB2 mutations in colorectal tumors with microsatellite instability10, and targeted inactivation of both alleles of EphB2 or EphB3, or a single allele of EphB4, significantly accelerate the tumorigenic process initiated by Apc mutations in mouse models8, 33. The gene discussed is EPHB2; the disease is colorectal neoplasm.