Recently, as our understanding of these events has increased, it has been demonstrated that the non-CpG methylation is not restricted to pluripotent cells; for example, non-CpG methylation can be particularly abundant in mouse and human brain tissue, which provides theoretical evidence for us to further study non-CpG methylation within the HIF-1α gene promoter in breast cancer cells. The gene discussed is HIF1A; the disease is breast cancer.