ID4 and breast cancer: Among the 340 under-expressed genes containing the 586 hyper-methylated CpGs, there were several tumor suppressor genes with under-expression that has previously been observed in breast cancer, such as L3MBTL4 [53], ID4 [54], RUNX3 [55, 56], PROX1 [57], SFRP1 [58] and others.