Objective: In recent decades, multiple therapeutics targeting the estrogen and human epidermal growth factor-2 (HER2) receptors have been approved for the treatment of breast cancer.
Methods: This review discusses a number of growth factor pathways that have been implicated in resistance to both anti-estrogen and HER2-targeted therapies. The association between growth factors and breast cancer is well established. Over decades, numerous laboratories have studied the link between insulin-like growth factor (IGF), insulin, and growth hormone (GH) to the development and progression of breast cancer.
Results: Although preclinical data demonstrates that blockade of these receptors inhibits breast cancer growth, progression, and drug resistance, therapies targeting the IGF, insulin, and GH receptors (GHRs) have not been successful in producing significant increases in progression-free, disease-free, or overall survival for patients with breast cancer. The failure to demonstrate a benefit of growth factor blockade in clinical trials can be attributed to redundancy in IGF, insulin, and GHR signaling pathways. All 3 receptors are able to activate oncogenic phosphoinositide-3 kinase (PI3K) and mitogen-activated protein kinase (MAPK) pathways.
Conclusion: Consequently, multitargeted blockade of growth factor receptors and their common downstream kinases will be necessary for the successful treatment of breast cancer.