SFRP2 and osteosarcoma: The SFRP2 promotor has been described to be (hyper)methylated in bladder cancer [45], breast cancer [46], cervical cancer [47], CRC [48], esophageal cancer [49], gallbladder cancer [50], gastric cancer [51], HCC [52], lung cancer [53], ovarian cancer [54], pancreatic cancer [55], prostate cancer [56], endometrial cancer [57], osteosarcoma [58], oral carcinoma [43], skin cancer [59], and brain tumors [60].