SOSTDC1 and breast cancer: One identified gene, sclerostin domain-containing protein 1 (SOSTDC1) was of particular interest, because SOSTDC1 showed a higher methylation level in breast cancer tissues than the other 13 genes (Additional file 6: Table S1) and among the three genes with the highest significant levels (KCNJ2, CELSR3 and SOSTDC1), SOSTDC1 was the only gene that has been reported to be associated with metastatic survival of breast cancer [22, 23], which indicates that SOSTDC1 plays a complex role in metastatic breast cancer, so we chose SOSTDC1 for further study.