ERBB4 and colorectal carcinoma: The decreased transcript levels of ERBB4 previously reported in ERBB3-deficient intestinal tumors suggests that elevated apoptosis may be due to loss of ERBB3-ERBB4 heterodimers [23], consistent with experiments showing a requirement for ERBB3-ERBB4 heterodimer–dependent AKT pathway activation to prevent CRC cell apoptosis [23].