Although expression of the ErbB4
receptor tyrosine kinase in
breast cancer is generally regarded as a marker for favorable patient prognosis, controversial exceptions have been reported. Alternative splicing of ErbB4 pre-mRNAs results in the expression of distinct receptor
isoforms with differential susceptibility to enzymatic cleavage and different downstream signaling
protein recruitment potential that could affect
tumor progression in different ways. ErbB4
protein expression from nontransfected cells is generally low compared with ErbB1 in most cell lines, and much of our knowledge of the role of ErbB4 in
breast cancer is derived from the ectopic overexpression of the receptor in non-breast-derived cell lines. One of the primary functions of ErbB4 in vivo is in the maturation of mammary glands during pregnancy and lactation induction. Pregnancy and extended lactation durations have been correlated with reduced risk of
breast cancer, and the role of ErbB4 in
tumor suppression may therefore be linked with its role in lactation. Most reports are consistent with a role for ErbB4 in reversing growth stimuli triggered by other ErbB family members during puberty. In this report, we provide a systems-level examination of several reports highlighting the seemingly opposing roles of ErbB4 in
breast cancer and potential explanations for the discrepancies and draw the conclusion that future studies examining the function of ErbB4 in
breast cancer should also take into account the pregnancy history, lactation status, and
hormone supplementation or ablation history of the patient from whom the
tumor or
tumor cells are derived.