ID4 and neoplasm: Not only have known tumor suppressor genes like Cdkn2a (p16), Itga4 (α 4-integrin) [1], and Igfbp7 [2] been identified as targets of aberrant methylation in cancer by RLGS, but also novel tumor suppressor genes such as TCF21 [3], SLC5A8 [4], ID4 [5], BMP3B [6], and SOCS1 [7] have been identified by RLGS.