Although breast cancer is a heterogeneous disease that is challenging to characterize and treat, the recent explosion of genetic and epigenetic research may help improve these endeavors. In the present review, we use genetic diversity to characterize and classify different types of breast cancer. We also discuss genetic and epigenetic changes that are involved in the development of different breast cancer types and examine how these changes affect prognosis. It appears that while a combination of mutations and copy number changes determine the type of breast cancer, epigenetic alterations may be the primary initiators of cancer development. Understanding these critical biomarkers and molecular changes will advance our ability to effectively treat breast cancer. Next, we examine potential drug therapies directed at epigenetic changes, as such epigenetic drug treatments may prove useful for treating patient-specific tumors, breast cancer progenitor cells, and drug-resistant cells. Lastly, we discuss on mechanisms of carcinogenesis, including a novel hypothesis outlining the role of epigenetics in the development of cancer progenitor cells and metastasis. Overall, breast cancer subtypes may have a similar epigenetic signal that promotes cancer development, and treatment may be most effective if both epigenetic and genetic differences are targeted.
Keywords: Breast cancer; breast cancer progression; cancer; cancer progenitor cells; combination therapy; de-methylation; drug resistance; epigenetics; epithelial-mesenchymal transition (EMT); gene copy number; histone deacetylase inhibitors; histone modification; metastasis; methylation; mutation; oncogene; review; therapeutics; tumor suppressor genes.